As said in the question, international characters tend to download themselves and be shown in the main text. This might be unwanted for some international users who are rather used to be shown a question mark or unknown character instead, as maybe font downloading may not be wished at all for safety reasons. This is a minor problem, and I only encountered this by seeing the "Indian Rupees" sign replaced by the hindi symbol of it, instead of the familiar "Rs." abbreviation I was used to, but still a reminder to be careful with implementing Unicode.