Add Vietnamese (vi) as a community language option

Vietnamese is unavailable in Community language settings, causing the UI to fall back to English for Vietnamese community content. General Translation supports vi.

Ticket Info

• Community ID: 8f9c74d7-0acf-4d28-8bbf-0fec358245c8
• User email(s) for those affected: heart.beat@plyon.app

Issue details (include screenshots and steps taken): The selector currently offers English, es, fr, it, pt, de, pl, nl, ar, and hi. Recent locale additions changed the same 11 files and merged in under an hour. Featurebase request has 1 upvote.

Repro

Not attempted; this is a feature request.