[FEATURE] Add Vietnamese (vi) language support for ProtonPlus translation

**Is your feature request related to a problem? Please describe.**
I am unable to contribute Vietnamese translations to the ProtonPlus project on Weblate. The current project configuration does not allow users to manually initialize or add a new language.

**Describe the solution you'd like**
Please add/initialize the Vietnamese (vi) language to the ProtonPlus translation project on Weblate.