src/Tools/Setup/isabelle/setup/Build.java

             }
             finally {
                 System.setOut(out_orig);
                 System.setErr(err_orig);
             }
-            compiler_result(ok, out.toString(), "Scala sources");
+            compiler_result(ok, out.toString(StandardCharsets.UTF_8), "Scala sources");
         }
     }
 
     public static void compile_java_sources(
         Path target_dir, String more_options, List<Path> deps, List<Path> sources)