Thank you, the Choicescript games look great for this purpose!
However, I don’t unfortunately have much time to play around with the more complex games at the moment. I’d appreciate any tips on simple choice-based games with purely textual states and actions (i.e. no inventory, no health, no map, etc.) and multiple endings –– ideally similar to Saving John and Machine of Death in this regard and ideally in an HTML format (exported from one of the engines, probably). I’ll assign rewards to the various endings manually shoud they not be present in the game (their presence is just a bonus and would make it easier for me).
I’m looking to take a a few of these games and try some transfer learning (learn by playing all but one text-game and then observe the behaviour on the previously unseen game).
I managed to write a simple interactive parser/player for HTML choice-based games in Python that I plan to use. I have no idea why I didn’t do this from the start and instead tried to work with the source codes of various game engines 
Anyways, thank you all again for helping me out and I hope I’ll be able to share some results in about a month.