Add option to s elect language when composing a toot

[halnine]

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Mastodon has a great option of selecting and filtering toots by language. Users can select which language the toot is written in (there is no automatic language detection afaik).

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Expected behavior

Actual behavior

Steps to reproduce

Extra info

Android version: (version code here) 11 Network type:

• [ ] Cellular
• [ ] Wi-Fi

App version: (version code here) 4.1.8 Build variant:

• [ ] Google
• [x] F-Droid

Micro-blogging service:

• [ ] Twitter
• [ ] Fanfou
• [ ] GNU Social / StatusNet
• [x] Mastodon

App settings:

• [ ] Custom API
• [ ] Custom consumer key/secrets
• [ ] Official keys
• [ ] Using Thumbor
• [ ] Connected through proxy
• [ ] Media preview enabled