Hmm I do like NIP-37 as a possible solution..
A lot of (think) work is already done with ActivityPub
Discussion
Ideally, it needs to be implemented in some clients as part of their on-boarding process. Unfortunately, i think most clients even don't have clear/good on-boarding steps for new users. If user can pick their language preference (speak) correctly then we can use those with NIP-32 to include language tag in each notes. 😅
That’s a way indeed (NIP-32)
Also selecting a language when you write a note is a nice way (like many Mastodon clients which also could autodetect the lang from the written content)
Yes, i think i will prefer this way since not every posts always stay in one language. It just needs good UI so it won't bother common users. They can manually or use auto detected language as default language value before posting. NIP-32 allows regular notes to embed 'l tag' to mark the language