[feature] Better handling for post languages

[tsmethurst]

There a couple of things we could be doing for posts to better surface their language property, which we don't currently do:

• [feature] Support any valid BCP 47 tag as a posting language #2066
• [feature] Show language code of posts in web view of statuses, next to date, likes, boosts, etc #2065
• [feature] Use lang html attribute in HTML version of posts #2064
• [feature] Federate language of Notes etc in and out of GtS properly #1277
• [feature] More comprehensive language selection options for frontend/settings panel #2306

We should try and do some or all of these, to make GtS easier to use for folks who post/read posts in multiple different languages!

[VyrCossont]

Today's #2066 is also related to post languages.

[tevino]

Somewhat related: #1277
This one is from the previous year

[zordsdavini]

tried to change the language directly through db - didn't helped

[cass-dlcm]

Hi, I'd like to note that #2066 isn't fully resolved. While BCP 47 states the tag structure, it delegates listing the tags to the Language Subtag Registry, maintained by IANA.

There's language tags in that registry that aren't options in the GoToSocial backend.

I'd like to help work on this, but I'm unfamiliar with the project's code and would like some guidance on how to proceed.

[tsmethurst]

Ah really, darn. Can you reproduce an example where you want to set a language for a post via the API but the (valid) tag isn't parsed correctly?

I would expect that we can cover all "primary language" subtags, but "extended language" and "region" subtags might be spotty.

[cass-dlcm]

I've found that some languages are missing from the "default posting language" setting.
I have also found that I can post things in a language that's missing from that setting's options, but I don't know if the language tag in the post is preserved.

I sent this status using fedilab, should be tagged as being in Toki Pona. Can someone check that for me: https://fedi.cass-dlcm.dev/@cassdlcm/statuses/01HMRS1PWD3FDWM85JHR4WYMAA

[tsmethurst]

I've found that some languages are missing from the "default posting language" setting.

Ah right that/s known already. That "default posting language" dropdown is not exhaustive. See #2306

I sent this status using fedilab, should be tagged as being in Toki Pona. Can someone check that for me: https://fedi.cass-dlcm.dev/@cassdlcm/statuses/01HMRS1PWD3FDWM85JHR4WYMAA

Language should be federated correctly, this is from the AP json of that status:

  "contentMap": {
    "tok": "<p>toki!</p>"
  },

I see it doesn't show up on the web view of the status though.