I can only share my experience with a related issue, and my communication with support about it.
I was attempting to store emojis on a MySQL database. I had followed some guide that I found for how to set the charset, and was able to directly load emoji values into the database, externally from Appsheet. When viewing those records within Appsheet, those emojis displayed correctly. However if I attempted to save a record with an emoji character, or even if I edited an existing record with a working emoji, then the emoji disappeared. The eventual response I got back from Appsheet support was:
As you noticed by default MySQL doesn’t support emoji characters. We first noticed this when an AppSheet customer reported that their users were getting insert errors when adding text. The issue was that their end users were putting emojis in their text making it un-insertable in MySQL. To help with the default MySQL case we put in a fix to strip emojis from text when using a database.
Ideally we would detect the text format settings in MySQL and only remove emojis if the table doesn’t support them, but though that’s conceptually simple it actually requires a fair bit of code change on our side and isn’t something we can do quickly or easily. We can add this to the request list, but I can’t say when or if it would be addressed.
Now, whether or not this is the same issue in your case, I personally can’t tell you. But if I had to guess, it probably is.
I suppose having your native language’s characters be stored correctly is probably higher priority than storing emojis, so maybe you’ll have better luck?
I’ll respond to that support email again and point them to this post for you.