is Chinese selected anywhere in your Language choices?
- I checked and I don't have Chinese language settings on my system.
Installed any Fonts lately?
- I don't recall recently adding fonts but I've had this problem for months and may have at an earlier time. What should I look out for here?
To find out if it's system wide or user specific, try this...
Open System Preferences>Users & Groups, unlock the lock, click on the little plus icon, make a new admin account, log out & into the new account.
Does it work in the new account?
- I created a new admin account and created a .md file. It's kind in Finder is 'Markdown'