After pressing Add, a prompt asking which language to use will populate your screen. Choose the new language simply by clicking on it. Restart the Mac OS 10.9 machine for the language change to take place. This can be done by clicking on the Apple Menu an

How to Add & Change to a New Language to Mac OS X. You can add as many languages as you want, but in this walkthrough we’ll focus on just adding a second new language and changing to that as the new language default. From the Apple menu visit “Sys

If you want to use your Mac in a different language, or you’re live in a different region, then you can change it in OS X. When you do, it’ll display everything in your preferred language, currency, date format, and more.