Disabling a language eliminates it from the language selection list, and users cannot select it. It does not clear or delete any content that has already been created in that language.
Any system language can be disabled except the system default language.
From the navigation bar, click Administration.
From the Settings page under Appearance and Customization, click Languages.
Beside a language, click the button so it moves to Disabled. The language is disabled. (Takes about five minutes for this to happen.)