That's strange then. I could change both launcher and client language from German to English that way.
Please discard my previous message, I tried changing the launcher language to english, the game is now in english too.This is not working.
The game seems to be using the OS language as it's own.
Although my custom.misc file is set to english, I'm running a french version of Windows 7, thus the game's writings are in french.
I'd like to be able to play the game in english without having to change my Windows language.
open "%APPDATA%..\Local\Frontier Developments\Elite Dangerous\Options\Player\Custom.misc" with a text-editor and change
<Language Value="German" />
back to
<Language Value="English" />