Changing the default language for Office programs
It is not possible to change the language of the Office for Mac user interface (menu items, buttons, or other interface elements) or Help content. When you buy Office for Mac, you receive only the language that you purchased. Language packs and language interface packs are not available at this time.
Although you can't change the interface language, Office for Mac does provide proofing tools—such as spelling, thesaurus, grammar, and hyphenation support—in multiple languages.