Good morning Poussemousse,
which admin template do you use? And which browser do you use? Clear browser cache, often cases changes in CSS files only take effect after clearing the cache.
Big thanks for your translations! I see, that are the language files for front end (site), and that is the reason, why your BwPostman sill speaks English. The language files for back end (admin) you find at administrator/language/en-GB and - believe me - that is the very bigger part!
Localize does not change anything at your settings or language files whilst you edit the language files in localize. Localize is only an editor, that does nothing without you.
A remark to your language files: I suppose, you are working with windows editor. This editor saves files per default as windows ANSI, but Joomla needs language files as UTF-8 without BOM. That you can reach with following instructions:
board.gulli.com/thread/1618767-windows-e...-in-utf-8-speichern/
This site is in German, but the interesting part - point 1 - 3 of the box - is in English. In localize you don't have to care about coding of the files
!
Best wishes
Romana
P.S.: There is a second module called overview, which also have language files…