Now you can configure the language through portal.office.com in several different places:

Office (web) -> change through office.com > Word > Language (Word) 
Office (web)(sharepoint) -> change through office.com > delve -> Word (sharepoint, onedrive) 
Office (on-premise) -> office.com -> below search, install office apps, other install options -> Change Language, download & install (click-to-run-)