When you have received a radio message, hit the "m key" to read it.
You can have German voices and English text, I think the settings for this is under the sound option in the main menu of the game. Itīs so long since I used the those parts of the menus that I donīt really remember how they look, but have a look and try it, the German voices are so much better then the English even if you donīt understand a word