Translating phrases is an endless pain for me. Primarily I want to have all phrases translated the members might come across, the backend isn't important.

The question now, can I filter this in any way? Are there parts in the language key showing me if it's for front or backend? Any help / idea will be highly appreciated.  

Unfortunately not - many phrases are used in both areas interchangeably. There is no distinction at the code level between a front end or back end phrase.