The string files merely tell you what is what and how it operates. You could translate them but as far as I know it shouldn't affect the overall operation of the game.

As far as I know that is the way the game can be transferred back and forth between languages for those that can't read English. I do know that each mod can have its own string file which will override the game's original so I don't believe you should have any issues. Give it a try and see.

Your game is looking for String\german.str and most mods only include a english.str. Try making a copy of the english.str and rename it german.str or what ever file your game is using found in the games root String\ directory. Mods only can replace files used by the game engine and your german version is not even loading the mods english.str so having a copy of the string file will load the mods german.str but will be english text in game.`