Failure to save translations for legacy languages using REST

The problem is that we're now using Locale in XWikiDocument but in our REST code we convert from String to Locale and then back to String which causes issue when using one of the 3 legacy language codes. Here's an excerpt from the JDK's JavaDoc:

Locale's constructor has always converted three language codes to their earlier, obsoleted forms: he maps to iw, yi maps to ji, and id maps to in.

So for example: new Locale("he").toString() != "he"