That is a directory within the phplist code.
Sorry but it is still not very clear what you want to do.
In your example Vorname, Stadt, Land etc are probably what are called attributes, and the name cannot be translated. You can give an attribute a name in German, “Stadt” say, but there is no way to display that in French. phplist doesn’t support that.
If your application displays in French then it can display a translated label, which it needs to manage, but still needs to refer to the “Stadt” attribute when submitting the subscription form.