`languages.json` is inconsistent with the provided API languages

[Philipp000]

Currently, we have a languages.json file, which corresponds to the languages given in the labels.json file.
For the API however, we also have different languages for the menu data.
I think, it would be great, if the languages.json would represent both translations.

We could either add a field, which indicates, which part is available in which language.
Or I think it would be sufficient, to add english translations, and have everything in both languages available.

Another point: currently the language is provided as uppercase (e.g. DE), however, the directory for english translations is lower case en, ideally, there would be reference, which language is available at which end point.
I would propose to add add a field base_url.

Further, the language.json currently contains the field enum_name, I would rename this to name, as for the API user it should be irrelevant, whether the files were generated through enums, objects, classes, etc...
This would also apply for the lables.json, and the enum folder in general. But we can also leave it, as it is.