Aww thank you, TheLostLaura!
I'm very happy to hear you like the demo and characters! x'D
As for the program, I used Ren'Py. It's a free software you can download here:
https://www.renpy.org/latest.html
This is only for Visual Novels though. If you want a broader media (maybe for mobile games or anything else) you should try and learn Unity. I should too actually, but I'm just too lazy :'D
And yes! I have Konoi to thank for that! She/he fixed the Spanish for me when all I had was google translator x'D
Hope to see you again!
xoxo,
SweetChiel