Changing the system languages in Macs are really easy. So if your friends / parents aren’t comfortable with your English system, you can always switch the language to suite their needs. Below is a step by step guide that will show you how to change the system language in Mac OS X.
Step 4. To demonstrate this functionality, I will change my system language from English to Simplified Chinese. All I have to do is to change the language order by dragging the Simplified Chinese on top of English.
Note: You can find a lot more languages when you click on the Edit List button in the International settings, but not all of them can make changes to the system language. I think Mac OS X only carry mainstream languages.