fsmcas: As far as I know, this game has a fully voiced German version. I bought it on Steam and it was only English, but later the German version was published in retail. No language update in Steam, though. Also no German on GOG.com? :(
Unfortunately not, it's available only in English. The German synchronization was done and published by Daedalic and GOG as well as Stream are distributing the original version from Telltale. That's why they can't simply add the language, because Telltale has no rights to sell it. GOG would have to negotiate with Daedalic to offer the German version, which would on the other hand make things like sales unnecessary complicated for them.