Just kidding - you can change language in-game.
As far as I know, you can do it separately for voice and text which is even greater.
So here's how it works:
- GOG installation (including pre-download) downloaded by Galaxy or from My Account includes by default ALL subtitles available for the game and English voice-over
- at the time of release, as soon as the first patch is downloaded, you will be able to change game language in the Galaxy (it will download that voice-pack without removing English one, so you can always easily switch between your language and English :)
- language packs will be also available for download from the Account page - I'm not sure if they will be there exactly at the moment of release but that's the plan :)