Change Language in recovery mode Yesterday I traded my old iPhone 5s for a MacBook Air 11“ Mid 2011, running MacOS High Sierra 10.13.6.

This is my first Mac.

Only problem is, the MacBook was purchased in Turkey so its system language is turkish. However I‘m located in Germany and dont speak a word in turkish. 

The desktop is in german, so no problem there but i tried to reinstall MacOS (is that Even necessary, it was hardly used and I dont see any files from the previous owner?)

When I try to reinstall MacOS the machine restarts and it opens a window completely in turkish where I can select a Backup from Time Machine (Time Machine is the only English word in the window). I dont know what the rest of the buttons do. 

Question: How do I change the language of the OS (not the Desktop-Part of the OS but the part that runs when repairing/reinstalling?
You can try sudo "/System/Library/CoreServices/Language Chooser.app/Contents/MacOS/Language Chooser"
then choose the system language you want.

Update: I tested it myself.
The above command is only valid for "macOS", it will change the login screen and shutdown message etc.
And the language of "recovery mode" is not associated with "macOS".  

If you want to change the language of "recovery mode".
Just follow the picture,first click File(Dosya) then choose 'Change Language'.