Written language on the post & filtering of the timeline by written language

[loma-one]

Describe the feature you'd like

Written language on the post

When a contribution is created, it should be possible to add the written language to the content. The data should be stored as metadata and thus support a filtering of the timeline.

The language stored in the profile is always assumed as the start value.

The written language should be able to be changed individually before sending a new contribution. E.g. by a list of the country abbreviations (DE, EN, FR, US, etc.).

filtering of the timeline by written language

The timeline should support filtering by spoken language.
For this purpose, a selection can be made from the list of written languages.
If the filter is activated, only those posts are displayed that have the country abbreviation in the posts.
The filtering can be changed to neutral, so that all posts are displayed again.

Describe alternatives you've considered

Additional context

[loma-one]

Duplicate from #6063