src/Pure/System/standard_system.scala

 
 package isabelle
 
 import java.lang.System
 import java.util.regex.Pattern
-import java.util.Locale
 import java.net.URL
 import java.io.{File => JFile}
 
 import scala.util.matching.Regex
 

     if (Platform.is_windows) {
       val result_path = new StringBuilder
       val rest =
         posix_path match {
           case Cygdrive(drive, rest) =>
-            result_path ++= (drive.toUpperCase(Locale.ENGLISH) + ":" + JFile.separator)
+            result_path ++= (Library.uppercase(drive) + ":" + JFile.separator)
             rest
           case Named_Root(root, rest) =>
             result_path ++= JFile.separator
             result_path ++= JFile.separator
             result_path ++= root

   def posix_path(jvm_path: String): String =
     if (Platform.is_windows) {
       jvm_path.replace('/', '\\') match {
         case Platform_Root(rest) => "/" + rest.replace('\\', '/')
         case Drive(letter, rest) =>
-          "/cygdrive/" + letter.toLowerCase(Locale.ENGLISH) +
+          "/cygdrive/" + Library.lowercase(letter) +
             (if (rest == "") "" else "/" + rest.replace('\\', '/'))
         case path => path.replace('\\', '/')
       }
     }
     else jvm_path