Thanks for your reply!
So I have Traditional Chinese added in the Preferred Languages section of Language & Region (just beneath English in the priority order) but find that Avid still converts all Chinese characters to question marks. The same happens if I change the Keyboard Input Sources to Chinese (from Keyboard settings in System Preferences).
As a test, I restarted my system with Traditional Chinese as the primary language. Now when importing these files, Avid is able to preserve the Chinese characters. However, once I switch the primary language for the system back to English, when I reopen Avid all the Chinese characters have switched to other symbols, like “ºAªL.∂¬¶Y∂¬.≤_™Œ¶œ ™Ùº›πƒ∂¿™”.
I’ve also tried a number of different fonts within Avid, such as Arial Unicode MS, which has a good track record of working in different languages, but haven’t had any success.
So I’m still looking for a solution here, will keep experimenting.