I have a product key and the Office Mac 2011 downloaded in French. Might it be possible to change the language interface from French into English or Russian? On this purpose, should I delete the current version and then download the Office again
using the same product key but choosing another language? Thanks beforehand.
Office for Mac 2011 does not have language packs and the ability to change the user interface as the Windows versions do. It's not available at the moment.
You need to uninstall your current version and download the Office again.