Auto-detect language when no language is provided when posting

[buresdv]

Is your proposal related to a problem?

When using the API, I've discovered that you are sometimes required to set the correct language when attempting to post (related to #2869). This means that some API requests might fail.

Describe the solution you'd like

A solution could be to have the backend recognize a post's language in case one isn't provided with the API request / set in the UI. This can be optional.

Describe alternatives you've considered

One solution that I wanted to use for Mlem was to use the iPhone's on-devide neural cores to detect a language of a post and automatically set it for each API request. This is, however, somewhat energy-draining and takes time, which is detrimental to the UX of the app. It is also extra work that is probably better suited for the backend, considering that a server has more computational power than a phone.

Additional context

None.