Yes, there will be a Steam release (as well as GOG, Gamergate, etc, and through the
Larian Vault).
Currently the only localizations confirmed are English, French, German, Polish and Russian, but other languages may be added. I don't know if there will be any tools released or support given to help with fan made translations (Larian seemed open to that idea for Divinity Original Sin, when it was suggested for Italian and Spanish translations, if other potential methods for an official release could not be arranged).
