I'm running the game with ScummVM 2.2.0, which allows to choose "voice AND text" in the Audio settings.
But there don't seem to be subtitles (switched the TV on).

Thanks for suggestions!

Subtitles are dependant on the game in question supporting them. Since in Starship Titanic, once you get the PET all conversation text appears in it automatically, the game didn't bother with subtitles for the other stuff right at the start of the game.

Thanks for answering, yes, later on the conversations are represented textually. But no complete subtitles.
All in all, a confusing game (and therefore not much fun). It doesn't know if it wants to be a parody or a game or a visual short story, it seems.