How to change language in Mac OS X Yosemite, El Capitan..
If you don't understand the existing language that used in your Mac OS X, you can follow the steps below by seeing the capture with arrow to change the language.
1. Click gear icon (System Preferences)
2. Choose Flag icon (Language & Region)
3. If you see your language in this list, just move it up to change to your language.
If you don't see, click the + to add your language.
4. Choose your language, in example I choose English.
6. Click X to exit
7. Will ask for restart the computer, click right button to restart.