This does not solve the issue. deselected by default here. Have had this issue using gmail in Safari only forever.
Got over it in the past by using Firefox - now with retina screen and firefox slow on the update, I am again getting question marks to replace Chinese text in attachments from gmail downloaded in Safari alone.
Same issue here! Unsolved after YEARS of this issue.
I dig through the downloads folder and paste a copied file name at least 15 times a day.
And Mountain Lion was supposed to be a big push for Chinese language users. Still a fail.
Really want to be a Safari supporter - would love to see this solved, Apple.