Fix lang generator escaping newlines, add lang generator test

src/main/java/net/minecraftforge/common/data/LanguageProvider.java

@@ -27,7 +27,7 @@ import java.util.Objects;
 import java.util.TreeMap;
 import java.util.function.Supplier;
 
-import org.apache.commons.lang3.StringEscapeUtils;
+import org.apache.commons.lang3.text.translate.JavaUnicodeEscaper;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -73,7 +73,7 @@ public abstract class LanguageProvider implements IDataProvider {
 
     private void save(DirectoryCache cache, Object object, Path target) throws IOException {
         String data = GSON.toJson(object);
-        data = StringEscapeUtils.escapeJava(data); // Escape control chars and unicode
+        data = JavaUnicodeEscaper.outsideOf(0, 0x7f).translate(data); // Escape unicode after the fact so that it's not double escaped by GSON
         String hash = IDataProvider.HASH_FUNCTION.hashUnencodedChars(data).toString();
         if (!Objects.equals(cache.getPreviousHash(target), hash) || !Files.exists(target)) {
            Files.createDirectories(target.getParent());