Update translations

[dennmuel]

After the wording has been reviewed we need to update at least the english and german translation files.
For further languages we will need community support.

[zuphilip]

We can try to get community support from within our course, as we did before. Would be good then to have some details about the status of the translations. Not sure if https://github.com/UB-Mannheim/PalMA/blob/master/locale/README.md is still up-to-date or there are better ways to show the current status.

[stweil]

The status will be updated when the new code goes into production. Then the German and English texts must be available. It would be difficult to get other translations until then, so those translations will come later.

[dennmuel]

German and English is done (but should be proof-read). As mentioned, further language may follow after the release.

[wagneral]

German and English has been proof-read, some smaller corrections have been made. Languages (de, en) are ok.

[stweil]

The current status of the translations shows that a lot of texts are still missing.

In addition, new languages can always be added.

Therefore I reopen this issue.