Hey there, glad to hear you enjoyed the game.
1. Yes, a full harem (Liza, Bella, Rachel and Susan) is possible without any negative consequences.
2. The Belugio ending is the canonical one. There's a different ending where you stay, but that's only when you don't romance anyone. There are variations in the ending though, depending who you take with you to Belugio (Liza, Bella, Rachel, Susan, Riley and Iris)
3. Always interested in getting it translated into to more languages. The files are available for a number of languages on Github, if you want to tackle one that isn't there just let me know and I'll generate the necessary files.