|Changing Ubuntu's regional settings|
From the Dash search for Language Support. Under the Regional Formats tab, you can set the preferred language. Click Apply System Wide if you want all accounts to be affected by this change. You can see a sample of how the new format looks like at the bottom.
If the language you want isn't on the list you can install it by clicking Install/Remove Languages from the Language tab.
The new settings will only take effect the next time you login.