Office Multi-Language Packs are available at no cost if you have a license for an Office suite. Office Multi-Language Packs are add-in products that can display the user interface of the Office desktop applications — windows, tabs, help, and so on — in more than 40 different languages. These packs also allow you to check spelling and grammar and use other proofing tools on documents created in these languages.
To get the Office Multi-Language Pack, click Software Assurance from the navigation bar on the Volume Licensing Centre, then Office Multi Language Packs. You'll need to have a license for an Office suite, not just an individual Office product.