[feature] Language filtering

[VyrCossont]

Is your feature request related to a problem ?

As an English and Spanish speaker, I want to see posts in those languages, but not in German or Chinese or other languages that I can't read.

Describe the solution you'd like.

Mastodon's approach

When you follow an account, you can provide a language list so you only see posts in those languages from that account.

You can also set a preference for only showing specific languages when viewing public timelines:

There doesn't seem to be an API for this second thing.

Note that Mastodon's language matching is rather basic (or it was last I checked) and is only aware of the ISO 639 part of a BCP 47 language tag, with the possible exception of traditional vs. simplified Mandarin Chinese.

Improving on this

Personally, the way I'd do it is with a user-level language_filters preference that applies to both home/list and public/tag timelines (but not search, thread contexts, notifications, or account timelines). This would take RFC 4647 extended language filters, although UX-wise we could start with a list of checkboxes from the same list we use for posting language.

We could implement follow-specific filtering as well, for cases where someone wants to see every language on their timeline but maybe doesn't care about a specific follow's frequent posts in a language they don't speak; I'd use the Mastodon API but extend it to also accept language filters.

Describe alternatives you've considered.

As with most Fedi features, it could be done client-side, but everything's more expensive on the client.

Additional context.

No response