Help with Making custom translations for UI

I want to translate Snap! to Tagalog, since I live in the Philippines, but I ran into some issues:

Custom Language Appearing in English:
Custom Language showing as Euskara while in other langauges (this might not matter, but the changes are: using copied Netherland's in locale.js and using a copied lang_eu):

Some parts of the menu don't work.

Using "Flat Design" gives me this error:

Is there an official way to make Translations in Snap!, or a proper way to do it? Please help!

how to translate snap:

Thanks! I should really start scanning the Snap! documents for info next time...