Add option to s elect language when composing a toot

[halnine]

Check before submitting issue -- Thank you!

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
• F-Droid

Micro-blogging service:

• Twitter
• Fanfou
• GNU Social / StatusNet
• Mastodon

App settings:

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