you can change the language whenever you want to:
- just go to "System Preferences",
- then go to "International" in the personal section,
- you will see a list with languages, drag your desired language to the top.
- then log out or restart the computer so then will the changes take effect.
(note: i just changed mine from spannish to english, and the clock still says the date in spannish , but that something i have customized, so i guess if you change those setting...