If you have tried every method for and the game stubbornly displays Russian or Polish (common with grey-market keys), you have two final options:
C:\Program Files (x86)\Steam\steamapps\common\Silent Hunter 5\
Here is the process to switch them:
Alternatively, locate SH5\Data\Sound\Speech , back up your English files, and replace them with the files from the German folder. Manual Configuration & Mods
How to Change the Language in Silent Hunter 5 : Battle of the Atlantic silent hunter 5 change language
Did we miss a method? Visit the Subsim.com forums, where the SH5 modding community has documented every language file in the game.
Navigate to your main game directory.
If the launcher is missing or bugged, you can manually force the game to run in a specific language by editing the main.cfg file. This is the most reliable method for Steam users.