Exclude legacy codes and fix deprecation for language handling

This change ensure uniqueness of returned languages and prevents using legacy language codes for templates.

Duplicates for locales with a legacy code were previously included since Java includes and maps them to correct locale: he maps to iw, yi maps to ji, and id maps to in.

The use of Locales constructor is deprecated.

See: https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/Locale.html#legacy_language_codes