How to fix font issue on gimp with x11 or macbook pro
GIMP automatically detects and uses the system language. 

In the unlikely event that language detection fails, or if you just want to use a different language, you may do so:

Apple Mac OS X

From System Preferences, click on the International icon. 


In the Language tab, the desired language should be the first in the list.


recent builds of GIMP may offer a language selection in the preferences