Post language should federate

[o-simardcasanova-net]

Both Bluesky and Mastodon support post languages, i.e., the user can set the language(s) in which a post is written.

Bridgy should federate this metadata, as not federating the language may greatly impact the visibility of posts that are not written in English.

From this conversation on Bluesky: https://bsky.app/profile/o.simardcasanova.net/post/3kuvhhogdp22x

[ikke-t]

In addition to visibility, also transalte button in mastodon clients don't work properly due getting wrong language from post metadata.

[snarfed]

In Bluesky, looks like this is the top-level langs array in app.bsky.feed.post, which has two-letter ISO_639-1 language codes:

          "langs": {
            "type": "array",
            "description": "Indicates human language of post primary text content.",
            "maxLength": 3,
            "items": { "type": "string", "format": "language" }
          }

Example posts:

• https://bsky.app/profile/o.simardcasanova.net/post/3kwkeewu26s22
• https://bsky.app/profile/o.simardcasanova.net/post/3kwkeeudh3k22

In AS2, it's the top-level contentMap field, a mapping from ISO 639-1 language code to full content. We added that in #681.

[snarfed]

Done! Examples:

• https://bsky.app/profile/snarfed.bsky.social/post/3kwxjrbrgb22q => https://indieweb.social/@snarfed.bsky.social@bsky.brid.gy/112764486613536842
• https://indieweb.social/@snarfed/112764489851370785 => https://bsky.app/profile/snarfed.indieweb.social.ap.brid.gy/post/3kwxjt5vpzcy2

[snarfed]

Thanks for the nudge here, all! Very good idea.