Well now that is mysterious!
Please excuse my complete beginner Thai writing. I was on the fence about doing it to begin with, but I figured if the conceit is that Mapel is getting strange mail from me, then I probably would have tried to practice writing the return address in crudely lettered Thai (in addition to whatever language they use on Moonsprout).
In my mind, the English (and Japanese) versions of Moonsprout are definitely a translation from some language, but I need to learn a bit more about language development before I can decide more details about it. If you (or a friend) have any good resources to learn about languages in island communities with one or more indigenous cultures and long-term cultural exchange through boat travel, let me know!