Maybe this helps:
Here's how to change your Xbox Live account language:
Go to Billing Account Information.
Sign in using your Microsoft account.
If multiple languages are supported for your country or region, select a language from Preferred Language.
Note The Preferred Language option does not appear if only one language is supported (for example, in the United States).
Click Save.
support.xbox.com/en-US/xbox-360/system/dashboard-or-hub-in-another-language
