Help with foreign languages

I've wondered about that. too. I'm working on a story set in Thailand.

I had the same problem with some Turkish characters. They were fine in Word but when transferred to TNBW I ended up with the question marks. Fortunately, there was a workaround for me--not as good as the original, but it sufficed. I just substituted the closest English letters to what was needed. Most people probably wouldn't catch the difference unless they know the language.

There are standards for handling this, but there are also variations that various people/organizations use.  The canonical response to a violation of the standard is to drop the suspect character, because if two different readers interpret it differently, the difference might open a security hole.  What you're seeing is not a drop, but a translation of the character to a question mark, though even that might open a security hole.

Unfortunately, Microsoft is not known for strict adherence to standards.  I don't know what library TNBW is using, but it too might decide that non-latin characters (including the barred symbols used by some latin-character Slavic languages) are unsafe.

I suspect that the transfer is made using HTML, which should be unambiguous even though Microsoft violates the standards left, right, east, west, in, out, and six times on Sunday.  That means that TNBW ought to be able to handle it.  But depending on how well the code base is organized by separation of concerns, it might be a hellacious fix with lots of problems introduced mid-flight.