I am not sure how to reset fonts in the OS to their defaults but i do suggest checking all the fonts you currently have for problems, here is how:
Open FontBook in the Applications folder.
Select all fonts in the first column.
Click 1 font in the 2nd column then select them all by pressing the Option (and) A keys.
next go to the File menu and select "validate fonts" this will check all your currently installed fonts for problems, might narrow things down.
Sorry at the moment i don't but i'll ask around and in the mean time maybe someone else will come with a more usefull post 🙂
At least you now know your font library is OK 🙂
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My Display Fonts are all Messed up!
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