diff --git a/htroot/ConfigHeuristics_p.java b/htroot/ConfigHeuristics_p.java
index c53fee68f..29d3ff2b1 100644
--- a/htroot/ConfigHeuristics_p.java
+++ b/htroot/ConfigHeuristics_p.java
@@ -39,6 +39,7 @@ import net.yacy.search.Switchboard;
 import java.io.IOException;
 import java.net.MalformedURLException;
 import java.util.Iterator;
+import java.util.Locale;
 
 import net.yacy.cora.document.id.MultiProtocolURL;
 import net.yacy.cora.federate.FederateSearchManager;
@@ -101,7 +102,7 @@ public class ConfigHeuristics_p {
                 // add new entry to config file
                 final String tmpname = post.get("ossys_newtitle");
                 if (tmpname != null && tmpurl !=null) {
-                    if (!tmpname.isEmpty() && !tmpurl.isEmpty() && tmpurl.toLowerCase().contains("{searchterms}")) {
+                    if (!tmpname.isEmpty() && !tmpurl.isEmpty() && tmpurl.toLowerCase(Locale.ROOT).contains("{searchterms}")) {
                      	/* Check eventual robots.txt policy */
                       	RobotsTxtEntry robotsEntry = null;
 						try {
diff --git a/htroot/Crawler_p.java b/htroot/Crawler_p.java
index b8b249688..a747cd52e 100644
--- a/htroot/Crawler_p.java
+++ b/htroot/Crawler_p.java
@@ -29,6 +29,7 @@ import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.regex.Pattern;
@@ -683,8 +684,8 @@ public class Crawler_p {
             try {
                 wantedPPM = post.getInt("customPPM", wantedPPM);
             } catch (final NumberFormatException e) {}
-            if ("minimum".equals(crawlingPerformance.toLowerCase())) wantedPPM = 10;
-            if ("maximum".equals(crawlingPerformance.toLowerCase())) wantedPPM = 30000;
+            if ("minimum".equals(crawlingPerformance.toLowerCase(Locale.ROOT))) wantedPPM = 10;
+            if ("maximum".equals(crawlingPerformance.toLowerCase(Locale.ROOT))) wantedPPM = 30000;
             
             int wPPM = wantedPPM;
             if ( wPPM <= 0 ) {
diff --git a/htroot/api/blacklists/add_entry_p.java b/htroot/api/blacklists/add_entry_p.java
index cb135deab..fc157df37 100644
--- a/htroot/api/blacklists/add_entry_p.java
+++ b/htroot/api/blacklists/add_entry_p.java
@@ -1,3 +1,5 @@
+import java.util.Locale;
+
 import net.yacy.cora.protocol.RequestHeader;
 import net.yacy.data.ListManager;
 import net.yacy.data.WorkTables;
@@ -25,7 +27,7 @@ public class add_entry_p {
 
             ListManager.switchboard.tables.recordAPICall(
             		post,
-            		"add_entry_p." + header.fileType().toString().toLowerCase(),
+            		"add_entry_p." + header.fileType().toString().toLowerCase(Locale.ROOT),
             		WorkTables.TABLE_API_TYPE_CONFIGURATION,
 					"add to blacklist '" + blacklistToUse + "': " + entry);
             
diff --git a/htroot/api/blacklists/delete_entry_p.java b/htroot/api/blacklists/delete_entry_p.java
index debf3dc23..9afa3b4f2 100644
--- a/htroot/api/blacklists/delete_entry_p.java
+++ b/htroot/api/blacklists/delete_entry_p.java
@@ -1,3 +1,5 @@
+import java.util.Locale;
+
 import net.yacy.cora.protocol.RequestHeader;
 import net.yacy.data.ListManager;
 import net.yacy.data.WorkTables;
@@ -26,7 +28,7 @@ public class delete_entry_p {
             // store this call as api call
             ListManager.switchboard.tables.recordAPICall(
             		post,
-            		"delete_entry_p." + header.fileType().toString().toLowerCase(),
+            		"delete_entry_p." + header.fileType().toString().toLowerCase(Locale.ROOT),
             		WorkTables.TABLE_API_TYPE_CONFIGURATION,
 					"delete from blacklist '" + blacklistToUse + "': " + entry);
 
diff --git a/htroot/api/getpageinfo_p.java b/htroot/api/getpageinfo_p.java
index 51b6f2bb8..a24f3ccc5 100644
--- a/htroot/api/getpageinfo_p.java
+++ b/htroot/api/getpageinfo_p.java
@@ -30,6 +30,7 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
 import java.util.Set;
 
 import javax.xml.parsers.DocumentBuilder;
@@ -116,7 +117,7 @@ public class getpageinfo_p {
             if (post.containsKey("actions"))
                 actions=post.get("actions");
             String url=post.get("url");
-			if (url.toLowerCase().startsWith("ftp://")) {
+			if (url.toLowerCase(Locale.ROOT).startsWith("ftp://")) {
 				prop.put("robots-allowed", "1"); // ok to crawl
 		        prop.put("robotsInfo", "ftp does not follow robots.txt");
 				prop.putXML("title", "FTP: " + url);
diff --git a/htroot/api/ymarks/add_ymark.java b/htroot/api/ymarks/add_ymark.java
index c11755584..b079ae4f0 100644
--- a/htroot/api/ymarks/add_ymark.java
+++ b/htroot/api/ymarks/add_ymark.java
@@ -1,4 +1,5 @@
 import java.io.IOException;
+import java.util.Locale;
 
 import net.yacy.cora.document.id.DigestURL;
 import net.yacy.cora.protocol.ClientIdentification;
@@ -51,7 +52,7 @@ public class add_ymark {
 	        	String url = post.get(YMarkEntry.BOOKMARK.URL.key(),YMarkEntry.BOOKMARK.URL.deflt());
 				boolean hasProtocol = false;
 				for (final YMarkTables.PROTOCOLS p : YMarkTables.PROTOCOLS.values()) {
-					if(url.toLowerCase().startsWith(p.protocol())) {
+					if(url.toLowerCase(Locale.ROOT).startsWith(p.protocol())) {
 						hasProtocol = true;
 						break;
 					}
diff --git a/source/net/yacy/cora/protocol/RequestHeader.java b/source/net/yacy/cora/protocol/RequestHeader.java
index 8a4b38f55..62f0a0b41 100644
--- a/source/net/yacy/cora/protocol/RequestHeader.java
+++ b/source/net/yacy/cora/protocol/RequestHeader.java
@@ -129,7 +129,7 @@ public class RequestHeader extends HeaderFramework implements HttpServletRequest
     public FileType fileType() {
         String path = this.getPathInfo();
         if (path == null) return FileType.HTML;
-        path = path.toLowerCase();
+        path = path.toLowerCase(Locale.ROOT);
         if (path.endsWith(".json")) return FileType.JSON;
         if (path.endsWith(".xml")) return FileType.XML;
         if (path.endsWith(".rdf")) return FileType.XML;
diff --git a/source/net/yacy/cora/protocol/http/HTTPClient.java b/source/net/yacy/cora/protocol/http/HTTPClient.java
index a04acc09d..1f6e94e33 100644
--- a/source/net/yacy/cora/protocol/http/HTTPClient.java
+++ b/source/net/yacy/cora/protocol/http/HTTPClient.java
@@ -34,6 +34,7 @@ import java.security.KeyManagementException;
 import java.security.NoSuchAlgorithmException;
 import java.security.cert.CertificateException;
 import java.security.cert.X509Certificate;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
@@ -664,7 +665,7 @@ public class HTTPClient {
 				mimeType = contentType.getValue();
 
 				if (mimeType != null) {
-					mimeType = mimeType.trim().toLowerCase();
+					mimeType = mimeType.trim().toLowerCase(Locale.ROOT);
 
 					final int pos = mimeType.indexOf(';');
 					if(pos >= 0) {
diff --git a/source/net/yacy/crawler/retrieval/Response.java b/source/net/yacy/crawler/retrieval/Response.java
index e4d1f41d0..fe6b7f244 100644
--- a/source/net/yacy/crawler/retrieval/Response.java
+++ b/source/net/yacy/crawler/retrieval/Response.java
@@ -28,6 +28,7 @@ package net.yacy.crawler.retrieval;
 
 import java.nio.charset.StandardCharsets;
 import java.util.Date;
+import java.util.Locale;
 
 import net.yacy.cora.document.analysis.Classification;
 import net.yacy.cora.document.encoding.ASCII;
@@ -787,7 +788,7 @@ public class Response {
 
         String mimeType = this.responseHeader.getContentType();
         if (mimeType != null) {
-            mimeType = mimeType.trim().toLowerCase();
+            mimeType = mimeType.trim().toLowerCase(Locale.ROOT);
 
             final int pos = mimeType.indexOf(';');
             return ((pos < 0) ? mimeType : mimeType.substring(0, pos));
diff --git a/source/net/yacy/data/wiki/WikiCode.java b/source/net/yacy/data/wiki/WikiCode.java
index 1d5248713..f7b1f2bf4 100644
--- a/source/net/yacy/data/wiki/WikiCode.java
+++ b/source/net/yacy/data/wiki/WikiCode.java
@@ -30,6 +30,7 @@ import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.regex.Pattern;
 
@@ -1069,7 +1070,7 @@ public class WikiCode extends AbstractWikiParser implements WikiParser {
             }
             if(closeIndex > 0) {
             	final String content = processedLine.substring(openIndex + LEN_WIKI_OPEN_METADATA, closeIndex);
-            	if (content.toLowerCase().startsWith("coordinate")) {
+            	if (content.toLowerCase(Locale.ROOT).startsWith("coordinate")) {
             		// parse Geographical Coordinates as described in
             		// http://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style_%28dates_and_numbers%29#Geographical_coordinates
             		// looks like:
@@ -1087,7 +1088,7 @@ public class WikiCode extends AbstractWikiParser implements WikiParser {
             		String name = "";
             		try {
             			for (final String c : b) {
-            				if (c.toLowerCase().startsWith("name=")) {
+            				if (c.toLowerCase(Locale.ROOT).startsWith("name=")) {
             					name = c.substring(5);
             				}
             				if (c.toUpperCase().startsWith("NS=")) {
diff --git a/source/net/yacy/document/Document.java b/source/net/yacy/document/Document.java
index eed245baf..e75e84c63 100644
--- a/source/net/yacy/document/Document.java
+++ b/source/net/yacy/document/Document.java
@@ -44,6 +44,7 @@ import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.regex.Matcher;
@@ -565,8 +566,8 @@ dc_rights
                     continue;
                 }
 
-                final boolean noindex = url.getRelProperty().toLowerCase().indexOf("noindex",0) >= 0;
-                final boolean nofollow = url.getRelProperty().toLowerCase().indexOf("nofollow",0) >= 0;
+                final boolean noindex = url.getRelProperty().toLowerCase(Locale.ROOT).indexOf("noindex",0) >= 0;
+                final boolean nofollow = url.getRelProperty().toLowerCase(Locale.ROOT).indexOf("nofollow",0) >= 0;
                 if ((thishost == null && url.getHost() == null) ||
                     ((thishost != null && url.getHost() != null) &&
                      (url.getHost().endsWith(thishost) ||
@@ -578,9 +579,9 @@ dc_rights
                 extpos = u.lastIndexOf('.');
                 if (extpos > 0) {
                     if (((qpos = u.indexOf('?')) >= 0) && (qpos > extpos)) {
-                        ext = u.substring(extpos + 1, qpos).toLowerCase();
+                        ext = u.substring(extpos + 1, qpos).toLowerCase(Locale.ROOT);
                     } else {
-                        ext = u.substring(extpos + 1).toLowerCase();
+                        ext = u.substring(extpos + 1).toLowerCase(Locale.ROOT);
                     }
                     if (Classification.isMediaExtension(ext)) {
                         // this is not a normal anchor, its a media link
@@ -705,10 +706,10 @@ dc_rights
                 u = url.toNormalform(true);
 
                 // find start of a referenced http url
-                if ((pos = u.toLowerCase().indexOf("http://", 7)) > 0) { // 7 = skip the protocol part of the source url
+                if ((pos = u.toLowerCase(Locale.ROOT).indexOf("http://", 7)) > 0) { // 7 = skip the protocol part of the source url
                     i.remove();
                     u = u.substring(pos);
-                    while ((pos = u.toLowerCase().indexOf("http://", 7)) > 0)
+                    while ((pos = u.toLowerCase(Locale.ROOT).indexOf("http://", 7)) > 0)
                         u = u.substring(pos);
                     url = new AnchorURL(u);
                     if (!(v.containsKey(url)))
@@ -717,10 +718,10 @@ dc_rights
                 }
 
                 // find start of a referenced https url
-                if ((pos = u.toLowerCase().indexOf("https://", 7)) > 0) { // 7 = skip the protocol part of the source url
+                if ((pos = u.toLowerCase(Locale.ROOT).indexOf("https://", 7)) > 0) { // 7 = skip the protocol part of the source url
                     i.remove();
                     u = u.substring(pos);
-                    while ((pos = u.toLowerCase().indexOf("https://", 7)) > 0)
+                    while ((pos = u.toLowerCase(Locale.ROOT).indexOf("https://", 7)) > 0)
                         u = u.substring(pos);
                     url = new AnchorURL(u);
                     if (!(v.containsKey(url)))
@@ -728,10 +729,10 @@ dc_rights
                     continue loop;
                 }
                 
-                if ((pos = u.toLowerCase().indexOf("/www.", 11)) > 0) { // 11 = skip protocol part + www of source url "http://www."
+                if ((pos = u.toLowerCase(Locale.ROOT).indexOf("/www.", 11)) > 0) { // 11 = skip protocol part + www of source url "http://www."
                     i.remove();
                     u = url.getProtocol()+":/" + u.substring(pos);
-                    while ((pos = u.toLowerCase().indexOf("/www.", 11)) > 0)
+                    while ((pos = u.toLowerCase(Locale.ROOT).indexOf("/www.", 11)) > 0)
                         u = url.getProtocol()+":/" + u.substring(pos);
 
                     AnchorURL addurl = new AnchorURL(u);
diff --git a/source/net/yacy/document/content/SurrogateReader.java b/source/net/yacy/document/content/SurrogateReader.java
index ff0524d2f..8f23ebca6 100644
--- a/source/net/yacy/document/content/SurrogateReader.java
+++ b/source/net/yacy/document/content/SurrogateReader.java
@@ -32,6 +32,7 @@ import java.io.PushbackInputStream;
 import java.io.StringReader;
 import java.net.MalformedURLException;
 import java.nio.charset.StandardCharsets;
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.BlockingQueue;
@@ -220,7 +221,7 @@ public class SurrogateReader extends DefaultHandler implements Runnable {
     @Override
     public void startElement(final String uri, final String name, String tag, final Attributes atts) throws SAXException {
         if (tag == null) return;
-        tag = tag.toLowerCase();
+        tag = tag.toLowerCase(Locale.ROOT);
         if ("record".equals(tag) || "document".equals(tag) || "doc".equals(tag)) {
             this.dcEntry = new DCEntry();
         } else if ("element".equals(tag) || "str".equals(tag) || "int".equals(tag) || "bool".equals(tag) || "long".equals(tag)) {
@@ -239,7 +240,7 @@ public class SurrogateReader extends DefaultHandler implements Runnable {
     @Override
     public void endElement(final String uri, final String name, String tag) {
         if (tag == null) return;
-        tag = tag.toLowerCase();
+        tag = tag.toLowerCase(Locale.ROOT);
         if ("record".equals(tag) || "document".equals(tag) || "doc".equals(tag)) {
             try {
                 // check if url is in accepted domain
diff --git a/source/net/yacy/document/parser/html/TransformerWriter.java b/source/net/yacy/document/parser/html/TransformerWriter.java
index 8c745cdbc..202c6186d 100644
--- a/source/net/yacy/document/parser/html/TransformerWriter.java
+++ b/source/net/yacy/document/parser/html/TransformerWriter.java
@@ -37,6 +37,7 @@ import java.io.OutputStreamWriter;
 import java.io.Writer;
 import java.nio.charset.Charset;
 import java.util.Enumeration;
+import java.util.Locale;
 import java.util.Properties;
 import java.util.Stack;
 import net.yacy.document.parser.html.ContentScraper.TagName;
@@ -194,7 +195,7 @@ public final class TransformerWriter extends Writer {
         if (in[1] == '/') {
             // a closing tag
             tagend = tagEnd(in, 2);
-            tag = new String(in, 2, tagend - 2).toLowerCase();
+            tag = new String(in, 2, tagend - 2).toLowerCase(Locale.ROOT);
             final char[] text = new char[in.length - tagend - 1];
             System.arraycopy(in, tagend, text, 0, in.length - tagend - 1);
             return filterTag(text, quotechar, tag, false);
@@ -207,7 +208,7 @@ public final class TransformerWriter extends Writer {
 
         // an opening tag
         tagend = tagEnd(in, 1);
-        tag = new String(in, 1, tagend - 1).toLowerCase();
+        tag = new String(in, 1, tagend - 1).toLowerCase(Locale.ROOT);
         final char[] text = new char[in.length - tagend - 1];
         System.arraycopy(in, tagend, text, 0, in.length - tagend - 1);
         return filterTag(text, quotechar, tag, true);
diff --git a/source/net/yacy/document/parser/rdfa/impl/RDFaTripleImpl.java b/source/net/yacy/document/parser/rdfa/impl/RDFaTripleImpl.java
index a1998efa8..c852f0ecb 100644
--- a/source/net/yacy/document/parser/rdfa/impl/RDFaTripleImpl.java
+++ b/source/net/yacy/document/parser/rdfa/impl/RDFaTripleImpl.java
@@ -5,6 +5,8 @@ import java.io.File;
 import java.io.IOException;
 import java.io.Reader;
 import java.util.ArrayList;
+import java.util.Locale;
+
 import javax.xml.transform.Templates;
 import javax.xml.transform.Transformer;
 import javax.xml.transform.TransformerConfigurationException;
@@ -38,7 +40,7 @@ public class RDFaTripleImpl{
 		BufferedReader bufReader = new BufferedReader(in);
                 bufReader.mark(2048); // mark position for following reset
 		String readLine = bufReader.readLine();
-		if (!readLine.toLowerCase().contains("<!doctype")){
+		if (!readLine.toLowerCase(Locale.ROOT).contains("<!doctype")){
 			bufReader.reset();
 		}
 
diff --git a/source/net/yacy/gui/framework/Browser.java b/source/net/yacy/gui/framework/Browser.java
index c49235dfa..0b967c6ac 100644
--- a/source/net/yacy/gui/framework/Browser.java
+++ b/source/net/yacy/gui/framework/Browser.java
@@ -30,6 +30,7 @@ import java.io.IOException;
 import java.io.InputStreamReader;
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.util.Locale;
 import java.util.Properties;
 
 import net.yacy.cora.util.ConcurrentLog;
@@ -61,7 +62,7 @@ public class Browser {
     static {
         // check operation system type
         final Properties sysprop = System.getProperties();
-        final String sysname = sysprop.getProperty("os.name","").toLowerCase();
+        final String sysname = sysprop.getProperty("os.name","").toLowerCase(Locale.ROOT);
         if (sysname.startsWith("mac os x")) {
             systemOS = systemMacOSX;
         } else if (sysname.startsWith("mac os")) {
diff --git a/source/net/yacy/http/AbstractRemoteHandler.java b/source/net/yacy/http/AbstractRemoteHandler.java
index c5cd3cbe2..ed1b89c4a 100644
--- a/source/net/yacy/http/AbstractRemoteHandler.java
+++ b/source/net/yacy/http/AbstractRemoteHandler.java
@@ -27,6 +27,7 @@ package net.yacy.http;
 import java.io.IOException;
 import java.net.InetAddress;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.Set;
 import java.util.StringTokenizer;
 
@@ -143,7 +144,7 @@ abstract public class AbstractRemoteHandler extends ConnectHandler implements Ha
         }
         
         // check the blacklist
-        if (Switchboard.urlBlacklist.isListed(BlacklistType.PROXY, hostOnly.toLowerCase(), request.getPathInfo())) {
+        if (Switchboard.urlBlacklist.isListed(BlacklistType.PROXY, hostOnly.toLowerCase(Locale.ROOT), request.getPathInfo())) {
         	response.sendError(HttpServletResponse.SC_FORBIDDEN,
         			"URL '" + hostOnly + "' blocked by yacy proxy (blacklisted)");
             baseRequest.setHandled(true);
diff --git a/source/net/yacy/http/servlets/YaCyDefaultServlet.java b/source/net/yacy/http/servlets/YaCyDefaultServlet.java
index 327977269..a89535583 100644
--- a/source/net/yacy/http/servlets/YaCyDefaultServlet.java
+++ b/source/net/yacy/http/servlets/YaCyDefaultServlet.java
@@ -39,6 +39,7 @@ import java.util.AbstractMap;
 import java.util.Enumeration;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.Callable;
@@ -705,7 +706,7 @@ public class YaCyDefaultServlet extends HttpServlet  {
         	
     		/* Let's check this header has a valid value */
         	if("http".equals(protocolHeader) || "https".equals(protocolHeader)) {
-        		protocol = protocolHeader.toLowerCase();
+        		protocol = protocolHeader.toLowerCase(Locale.ROOT);
         	} else if(protocolHeader != null && !protocolHeader.isEmpty()) {
     			ConcurrentLog.warn("FILEHANDLER","YaCyDefaultServlet: illegal protocol scheme header value : " + protocolHeader);
     		}
@@ -713,7 +714,7 @@ public class YaCyDefaultServlet extends HttpServlet  {
     		/* This peer can also be behind a reverse proxy requested using https, even if the request coming to this YaCy peer is http only
     		 * Possible scenario (happens for example when YaCy is deployed on Heroku Platform) : User browser -> https://reverseProxy/yacyURL -> http://yacypeer/yacyURL
     		 * In that case, absolute URLs rendered by this peer (in rss feeds for example) must effectively start with the https scheme */
-        	protocolHeader = header.get(HttpHeaders.X_FORWARDED_PROTO.toString(), "").toLowerCase();
+        	protocolHeader = header.get(HttpHeaders.X_FORWARDED_PROTO.toString(), "").toLowerCase(Locale.ROOT);
         	
     		/* Here we only allow an upgrade from HTTP to HTTPS, not the reverse (we don't want a forged HTTP header by an eventual attacker to force fallback to HTTP) */
         	if("https".equals(protocolHeader)) {
diff --git a/source/net/yacy/kelondro/data/meta/URIMetadataNode.java b/source/net/yacy/kelondro/data/meta/URIMetadataNode.java
index 5ca31c85a..f63c80a6a 100644
--- a/source/net/yacy/kelondro/data/meta/URIMetadataNode.java
+++ b/source/net/yacy/kelondro/data/meta/URIMetadataNode.java
@@ -34,6 +34,7 @@ import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Properties;
 import java.util.Set;
 import java.util.regex.Pattern;
@@ -264,7 +265,7 @@ public class URIMetadataNode extends SolrDocument /* implements Comparable<URIMe
     public boolean matches(Pattern pattern) {
         return pattern.matcher(this.url.toNormalform(true)).matches();
         //CharacterRunAutomaton automaton = new CharacterRunAutomaton(matcher);
-        //boolean match = automaton.run(this.url.toNormalform(true).toLowerCase());
+        //boolean match = automaton.run(this.url.toNormalform(true).toLowerCase(Locale.ROOT));
         //return match;
     }
 
@@ -930,7 +931,7 @@ public class URIMetadataNode extends SolrDocument /* implements Comparable<URIMe
         if (this.alternative_urlstring != null) return this.alternative_urlstring;
         
         if (!pdfParser.individualPages) return this.url().toNormalform(true);
-        if (!"pdf".equals(MultiProtocolURL.getFileExtension(this.url().getFileName()).toLowerCase())) return this.url().toNormalform(true);
+        if (!"pdf".equals(MultiProtocolURL.getFileExtension(this.url().getFileName()).toLowerCase(Locale.ROOT))) return this.url().toNormalform(true);
         // for pdf links we rewrite the url
         // this is a special treatment of pdf files which can be splitted into subpages
         String pageprop = pdfParser.individualPagePropertyname;
diff --git a/source/net/yacy/kelondro/util/Formatter.java b/source/net/yacy/kelondro/util/Formatter.java
index 52432b951..07ee3401e 100644
--- a/source/net/yacy/kelondro/util/Formatter.java
+++ b/source/net/yacy/kelondro/util/Formatter.java
@@ -77,7 +77,7 @@ public final class Formatter {
      * @param lang an ISO 639 language code which is used to generate a {@link Locale}
      */
     public static void setLocale(final String lang) {
-        final String l = (lang.equalsIgnoreCase("default") ? "en" : lang.toLowerCase());
+        final String l = (lang.equalsIgnoreCase("default") ? "en" : lang.toLowerCase(Locale.ROOT));
         setLocale(l.equals("none") ? null : new Locale(l));
     }
 
diff --git a/source/net/yacy/kelondro/util/ISO639.java b/source/net/yacy/kelondro/util/ISO639.java
index 526c1ec8b..52818f64b 100644
--- a/source/net/yacy/kelondro/util/ISO639.java
+++ b/source/net/yacy/kelondro/util/ISO639.java
@@ -26,6 +26,7 @@
 
 package net.yacy.kelondro.util;
 
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
@@ -183,7 +184,7 @@ public class ISO639 {
      * @return the name of the country
      */
     public static final String country(String code) {
-        return mapping.get(code.toLowerCase());
+        return mapping.get(code.toLowerCase(Locale.ROOT));
     }
     
     /**
@@ -192,7 +193,7 @@ public class ISO639 {
      * @return true if the code exists
      */
     public static final boolean exists(String code) {
-        return mapping.containsKey(code.toLowerCase());
+        return mapping.containsKey(code.toLowerCase(Locale.ROOT));
     }
     
     /**
@@ -202,7 +203,7 @@ public class ISO639 {
      */
     public static final String userAgentLanguageDetection(String userAgent) {
         if (userAgent == null || userAgent.length() < 2) return null;
-        userAgent = userAgent.toLowerCase();
+        userAgent = userAgent.toLowerCase(Locale.ROOT);
         if (mapping.containsKey(userAgent.substring(0, 2))) return userAgent.substring(0, 2);
         if (userAgent.length() == 2 && mapping.containsKey(userAgent)) return userAgent;
         if (userAgent.length() == 5 && mapping.containsKey(userAgent.substring(0, 2))) return userAgent.substring(0, 2);
diff --git a/source/net/yacy/kelondro/util/OS.java b/source/net/yacy/kelondro/util/OS.java
index 517563525..7913e6356 100644
--- a/source/net/yacy/kelondro/util/OS.java
+++ b/source/net/yacy/kelondro/util/OS.java
@@ -29,6 +29,7 @@ import java.lang.management.ManagementFactory;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
 
@@ -71,7 +72,7 @@ public final class OS {
 	static {
 		// check operation system type
 		final Properties sysprop = java.lang.System.getProperties();
-		final String sysname = sysprop.getProperty("os.name","").toLowerCase();
+		final String sysname = sysprop.getProperty("os.name","").toLowerCase(Locale.ROOT);
 		if (sysname.startsWith("mac os x")) systemOS = System.MacOSX;
 		else if (sysname.startsWith("mac os")) systemOS = System.MacOSC;
 		else if (sysname.startsWith("windows")) systemOS = System.Windows;
diff --git a/source/net/yacy/peers/Network.java b/source/net/yacy/peers/Network.java
index 25f4c90fe..32a26fc59 100644
--- a/source/net/yacy/peers/Network.java
+++ b/source/net/yacy/peers/Network.java
@@ -45,6 +45,7 @@ import java.util.HashMap;
 import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
@@ -601,7 +602,7 @@ public class Network
                 if ( seedURLStr.isEmpty() ) {
                     throw new MalformedURLException("The seed-file url must not be empty.");
                 }
-                if ( !(seedURLStr.toLowerCase().startsWith("http://") || seedURLStr.toLowerCase().startsWith(
+                if ( !(seedURLStr.toLowerCase(Locale.ROOT).startsWith("http://") || seedURLStr.toLowerCase(Locale.ROOT).startsWith(
                     "https://")) ) {
                     throw new MalformedURLException("Unsupported protocol.");
                 }
diff --git a/source/net/yacy/peers/operation/yacyRelease.java b/source/net/yacy/peers/operation/yacyRelease.java
index ad96c1406..d8a045740 100644
--- a/source/net/yacy/peers/operation/yacyRelease.java
+++ b/source/net/yacy/peers/operation/yacyRelease.java
@@ -39,6 +39,7 @@ import java.security.SignatureException;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.SortedSet;
 import java.util.TreeSet;
@@ -322,7 +323,7 @@ public final class yacyRelease extends yacyVersion {
             }
             final ResponseHeader header = response.getResponseHeader();
 
-            final boolean unzipped = header.gzip() && (header.mime().toLowerCase().equals("application/x-tar")); // if true, then the httpc has unzipped the file
+            final boolean unzipped = header.gzip() && (header.mime().toLowerCase(Locale.ROOT).equals("application/x-tar")); // if true, then the httpc has unzipped the file
             if (unzipped && name.endsWith(".tar.gz")) {
                 download = new File(storagePath, name.substring(0, name.length() - 3));
             } else {
diff --git a/source/net/yacy/search/index/Segment.java b/source/net/yacy/search/index/Segment.java
index 40eacc2bb..4d43f6dc6 100644
--- a/source/net/yacy/search/index/Segment.java
+++ b/source/net/yacy/search/index/Segment.java
@@ -33,6 +33,7 @@ import java.util.Collection;
 import java.util.Date;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ArrayBlockingQueue;
@@ -504,10 +505,10 @@ public class Segment {
                     // two possible results: compare and report conflicts
                     if (!language.equals(url.language())) {
                         // see if we have a hint in the url that the statistic was right
-                        final String u = urlNormalform.toLowerCase();
+                        final String u = urlNormalform.toLowerCase(Locale.ROOT);
                         String ISO639_country = ISO639.country(language);
                         if (u.contains("/" + language + "/") ||
-                            (ISO639_country != null && u.contains("/" + ISO639.country(language).toLowerCase() + "/"))) {
+                            (ISO639_country != null && u.contains("/" + ISO639.country(language).toLowerCase(Locale.ROOT) + "/"))) {
                             // this is a strong hint that the statistics was in fact correct
                         } else {
                             // no confirmation using the url, use the TLD
diff --git a/source/net/yacy/search/query/QueryModifier.java b/source/net/yacy/search/query/QueryModifier.java
index 54c9fc131..a4b75f34d 100644
--- a/source/net/yacy/search/query/QueryModifier.java
+++ b/source/net/yacy/search/query/QueryModifier.java
@@ -23,6 +23,7 @@ package net.yacy.search.query;
 import java.net.MalformedURLException;
 import java.util.ArrayList;
 import java.util.Date;
+import java.util.Locale;
 
 import org.apache.solr.common.params.CommonParams;
 import org.apache.solr.common.params.MultiMapSolrParams;
@@ -200,7 +201,7 @@ public class QueryModifier {
                 this.language = querystring.substring(langi + 10, langi + 12);
                 querystring = querystring.replace("/language/" + this.language, "");
                 if (this.language.length() == 2 && ISO639.exists(this.language)) { // only 2-digit codes valid
-                    this.language = this.language.toLowerCase();
+                    this.language = this.language.toLowerCase(Locale.ROOT);
                     add("/language/" + this.language);
                 } else {
                     this.language = null;
diff --git a/source/net/yacy/search/query/QueryParams.java b/source/net/yacy/search/query/QueryParams.java
index 98025a2e0..527631848 100644
--- a/source/net/yacy/search/query/QueryParams.java
+++ b/source/net/yacy/search/query/QueryParams.java
@@ -36,6 +36,7 @@ import java.util.HashMap;
 import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.SortedSet;
@@ -700,7 +701,7 @@ public final class QueryParams {
 
         StringBuilder sb = new StringBuilder(120);
         sb.append("yacysearch.");
-        sb.append(ext.name().toLowerCase());
+        sb.append(ext.name().toLowerCase(Locale.ROOT));
         sb.append("?query=");
 
         sb.append(theQuery.getQueryGoal().getQueryString(true));
diff --git a/source/net/yacy/search/schema/CollectionConfiguration.java b/source/net/yacy/search/schema/CollectionConfiguration.java
index c08d65cdf..070565cb3 100644
--- a/source/net/yacy/search/schema/CollectionConfiguration.java
+++ b/source/net/yacy/search/schema/CollectionConfiguration.java
@@ -40,6 +40,7 @@ import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.TreeMap;
@@ -302,7 +303,7 @@ public class CollectionConfiguration extends SchemaConfiguration implements Seri
         // path elements of link
         String filename = digestURL.getFileName();
         String extension = MultiProtocolURL.getFileExtension(filename);
-        String filenameStub = filename.toLowerCase().endsWith("." + extension) ? filename.substring(0, filename.length() - extension.length() - 1) : filename;
+        String filenameStub = filename.toLowerCase(Locale.ROOT).endsWith("." + extension) ? filename.substring(0, filename.length() - extension.length() - 1) : filename;
         // remove possible jsession (or other url parm like "img.jpg;jsession=123") 
         // TODO: consider to implement ";jsession=123" check in getFileExtension()
         if (extension.indexOf(';') >= 0) extension = extension.substring(0,extension.indexOf(';'));
@@ -632,7 +633,7 @@ public class CollectionConfiguration extends SchemaConfiguration implements Seri
             String robots_meta = html.getMetas().get("robots");
             // this tag may have values: all, index, noindex, nofollow; see http://www.robotstxt.org/meta.html
             if (robots_meta != null) {
-                robots_meta = robots_meta.toLowerCase();
+                robots_meta = robots_meta.toLowerCase(Locale.ROOT);
                 if (robots_meta.indexOf("all",0) >= 0) b += 1;      // set bit 0
                 if (robots_meta.indexOf("index",0) == 0 || robots_meta.indexOf(" index",0) >= 0 || robots_meta.indexOf(",index",0) >= 0 ) b += 2; // set bit 1
                 if (robots_meta.indexOf("follow",0) == 0 || robots_meta.indexOf(" follow",0) >= 0 || robots_meta.indexOf(",follow",0) >= 0 ) b += 4; // set bit 2
@@ -2166,7 +2167,7 @@ public class CollectionConfiguration extends SchemaConfiguration implements Seri
         List<Integer> il = new ArrayList<Integer>(rel.size());
         for (final String s: rel) {
             int i = 0;
-            final String s0 = s.toLowerCase().trim();
+            final String s0 = s.toLowerCase(Locale.ROOT).trim();
             if ("me".equals(s0)) i += 1;
             if ("nofollow".equals(s0)) i += 2;
             il.add(i);
diff --git a/source/net/yacy/search/schema/CollectionSchema.java b/source/net/yacy/search/schema/CollectionSchema.java
index 52a35e1b1..cdaf114c7 100644
--- a/source/net/yacy/search/schema/CollectionSchema.java
+++ b/source/net/yacy/search/schema/CollectionSchema.java
@@ -22,6 +22,7 @@ package net.yacy.search.schema;
 
 import java.util.Date;
 import java.util.List;
+import java.util.Locale;
 
 import net.yacy.cora.federate.solr.SchemaDeclaration;
 import net.yacy.cora.federate.solr.SolrType;
@@ -322,7 +323,7 @@ public enum CollectionSchema implements SchemaDeclaration {
     public final void setSolrFieldName(String theValue) {
         // make sure no empty string is assigned
         if ( (theValue != null) && (!theValue.isEmpty()) ) {
-            this.solrFieldName = theValue.toLowerCase();
+            this.solrFieldName = theValue.toLowerCase(Locale.ROOT);
         } else {
             this.solrFieldName = null;
         }
diff --git a/source/net/yacy/search/schema/WebgraphSchema.java b/source/net/yacy/search/schema/WebgraphSchema.java
index 9f4b6ad55..bd16245a1 100644
--- a/source/net/yacy/search/schema/WebgraphSchema.java
+++ b/source/net/yacy/search/schema/WebgraphSchema.java
@@ -22,6 +22,7 @@ package net.yacy.search.schema;
 
 import java.util.Date;
 import java.util.List;
+import java.util.Locale;
 
 import net.yacy.cora.federate.solr.SchemaDeclaration;
 import net.yacy.cora.federate.solr.SolrType;
@@ -155,7 +156,7 @@ public enum WebgraphSchema implements SchemaDeclaration {
     public final void setSolrFieldName(String theValue) {
         // make sure no empty string is assigned
         if ( (theValue != null) && (!theValue.isEmpty()) ) {
-            this.solrFieldName = theValue.toLowerCase();
+            this.solrFieldName = theValue.toLowerCase(Locale.ROOT);
         } else {
             this.solrFieldName = null;
         }
diff --git a/source/net/yacy/server/serverObjects.java b/source/net/yacy/server/serverObjects.java
index 68090c51f..39dc76515 100644
--- a/source/net/yacy/server/serverObjects.java
+++ b/source/net/yacy/server/serverObjects.java
@@ -55,6 +55,7 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.regex.Pattern;
@@ -480,7 +481,7 @@ public class serverObjects implements Serializable, Cloneable {
     public boolean getBoolean(final String key) {
         String s = removeByteOrderMark(get(key));
         if (s == null) return false;
-        s = s.toLowerCase();
+        s = s.toLowerCase(Locale.ROOT);
         return s.equals("true") || s.equals("on") || s.equals("1");
     }
 
diff --git a/source/net/yacy/utils/translation/TranslatorXliff.java b/source/net/yacy/utils/translation/TranslatorXliff.java
index 534433f71..a95c1d857 100644
--- a/source/net/yacy/utils/translation/TranslatorXliff.java
+++ b/source/net/yacy/utils/translation/TranslatorXliff.java
@@ -34,6 +34,7 @@ import java.io.IOException;
 import java.io.OutputStreamWriter;
 import java.nio.charset.StandardCharsets;
 import java.util.LinkedHashMap;
+import java.util.Locale;
 import java.util.Map;
 import java.util.TreeMap;
 import javax.xml.stream.XMLInputFactory;
@@ -163,7 +164,7 @@ public class TranslatorXliff extends Translator {
     @Override
     public Map<String, Map<String, String>> loadTranslationsLists(final File xliffFile) {
         File locallng = getScratchFile(xliffFile);
-        if (xliffFile.getName().toLowerCase().endsWith(".xlf") || xliffFile.getName().toLowerCase().endsWith(".xliff")) {
+        if (xliffFile.getName().toLowerCase(Locale.ROOT).endsWith(".xlf") || xliffFile.getName().toLowerCase(Locale.ROOT).endsWith(".xliff")) {
             if (locallng.exists()) {
                 Map<String, Map<String, String>> mergedList = loadTranslationsListsFromXliff(xliffFile);
                 Map<String, Map<String, String>> tmplist = loadTranslationsListsFromXliff(locallng);
diff --git a/source/net/yacy/yacy.java b/source/net/yacy/yacy.java
index 4c4690e32..052546161 100644
--- a/source/net/yacy/yacy.java
+++ b/source/net/yacy/yacy.java
@@ -40,6 +40,7 @@ import java.nio.channels.FileLock;
 import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
 import java.util.concurrent.Semaphore;
@@ -780,7 +781,7 @@ public final class yacy {
 	        // exception : if the -gui option is used then do not go into headless mode since that uses a gui
 	        boolean headless = true;
 	        if (OS.isWindows) headless = false;
-	        if (args.length >= 1 && args[0].toLowerCase().equals("-gui")) headless = false;
+	        if (args.length >= 1 && args[0].toLowerCase(Locale.ROOT).equals("-gui")) headless = false;
 	        System.setProperty("java.awt.headless", headless ? "true" : "false");
 
 	        String s = ""; for (final String a: args) s += a + " ";
@@ -790,32 +791,32 @@ public final class yacy {
 	        File dataRoot = applicationRoot;
 	        //System.out.println("args.length=" + args.length);
 	        //System.out.print("args=["); for (int i = 0; i < args.length; i++) System.out.print(args[i] + ", "); System.out.println("]");
-	        if ((args.length >= 1) && (args[0].toLowerCase().equals("-startup") || args[0].equals("-start"))) {
+	        if ((args.length >= 1) && (args[0].toLowerCase(Locale.ROOT).equals("-startup") || args[0].equals("-start"))) {
 	            // normal start-up of yacy
 	            if (args.length > 1) {
 	            	dataRoot = new File(System.getProperty("user.home").replace('\\', '/'), args[1]);
 	            }
                 preReadSavedConfigandInit(dataRoot);
 	            startup(dataRoot, applicationRoot, startupMemFree, startupMemTotal, false);
-	        } else if (args.length >= 1 && args[0].toLowerCase().equals("-gui")) {
+	        } else if (args.length >= 1 && args[0].toLowerCase(Locale.ROOT).equals("-gui")) {
 	            // start-up of yacy with gui
 	            if (args.length > 1) {
 	            	dataRoot = new File(System.getProperty("user.home").replace('\\', '/'), args[1]);
 	            }
                 preReadSavedConfigandInit(dataRoot);
 	            startup(dataRoot, applicationRoot, startupMemFree, startupMemTotal, true);
-	        } else if ((args.length >= 1) && ((args[0].toLowerCase().equals("-shutdown")) || (args[0].equals("-stop")))) {
+	        } else if ((args.length >= 1) && ((args[0].toLowerCase(Locale.ROOT).equals("-shutdown")) || (args[0].equals("-stop")))) {
 	            // normal shutdown of yacy
 	            if (args.length == 2) applicationRoot= new File(args[1]);
 	            shutdown(applicationRoot);
-	        } else if ((args.length >= 1) && (args[0].toLowerCase().equals("-update"))) {
+	        } else if ((args.length >= 1) && (args[0].toLowerCase(Locale.ROOT).equals("-update"))) {
 	            // aut-update yacy
 	            if (args.length == 2) applicationRoot= new File(args[1]);
 	            update(applicationRoot);
-	        } else if ((args.length >= 1) && (args[0].toLowerCase().equals("-version"))) {
+	        } else if ((args.length >= 1) && (args[0].toLowerCase(Locale.ROOT).equals("-version"))) {
 	            // show yacy version
 	            System.out.println(copyright);
-            } else if ((args.length > 1) && (args[0].toLowerCase().equals("-config"))) {
+            } else if ((args.length > 1) && (args[0].toLowerCase(Locale.ROOT).equals("-config"))) {
                     // set config parameter. Special handling of adminAccount=user:pwd (generates md5 encoded password)
                     // on Windows parameter should be enclosed in doublequotes to accept = sign (e.g. -config "port=8090" "port.ssl=8043")
                     File f = new File (dataRoot,"DATA/SETTINGS/");
diff --git a/test/java/net/yacy/document/parser/htmlParserTest.java b/test/java/net/yacy/document/parser/htmlParserTest.java
index a57c5b1c7..beb554a80 100644
--- a/test/java/net/yacy/document/parser/htmlParserTest.java
+++ b/test/java/net/yacy/document/parser/htmlParserTest.java
@@ -8,6 +8,8 @@ import java.net.MalformedURLException;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.util.List;
+import java.util.Locale;
+
 import junit.framework.TestCase;
 import net.yacy.cora.document.id.AnchorURL;
 import net.yacy.document.Document;
@@ -40,13 +42,13 @@ public class htmlParserTest extends TestCase {
 		for (int i=0; i < testStrings.length; i++) {
 			// desired conversion result
 			String shouldBe = testStrings[i][1];
-			shouldBe = shouldBe!=null ? shouldBe.toLowerCase() : null;
+			shouldBe = shouldBe!=null ? shouldBe.toLowerCase(Locale.ROOT) : null;
 			
 			// conversion result
 			String charset = htmlParser.patchCharsetEncoding(testStrings[i][0]);
 			
 			// test if equal
-			assertEquals(shouldBe, charset!=null ? charset.toLowerCase() : null);
+			assertEquals(shouldBe, charset!=null ? charset.toLowerCase(Locale.ROOT) : null);
 			System.out.println("testGetRealCharsetEncoding: " + (testStrings[i][0]!=null?testStrings[i][0]:"null") + " -> " + (charset!=null?charset:"null") + " | Supported: " + (charset!=null?Charset.isSupported(charset):false));
 			
 		}