Are any addons replacing fonts?
The thing is now in MoP you got 19 font files and not only the old 5 or 6. If you replace all fonts to one specific font then other non-latin languages will show up as "?" characters.
Code:
2002.ttf 2002 (Korean)
2002B.ttf 2002B (Korean)
ARHei.ttf AR CrystalzcuheiGBK Demibold (Chinese)
ARIALN.TTF Arial Narrow
ARKai_C.ttf AR ZhongkaiGBK Medium (Chinese)
ARKai_T.ttf AR ZhongkaiGBK Medium (Chinese)
bHEI00M.ttf AR Heiti2 Medium B5 (Chinese)
bHEI01B.ttf AR Heiti2 Bold B5 (Chinese)
bKAI00M.ttf AR Kaiti Medium B5 (Chinese)
bLEI00D.ttf AR Leisu Demi B5 (Chinese)
FRIZQT__.TTF Friz Quadrata TT (Latin)
FRIZQT___CYR.TTF FrizQuadrataCTT (Cyrilic)
K_Damage.TTF YDIWingsM (Korean)
K_Pagetext.TTF YDIMokM (Korean)
MORPHEUS.TTF Morpheus (Latin)
MORPHEUS_CYR.TTF Morpheus Cyr (Cyrilic)
NIM_____.ttf Nimrod MT (Unsure for what purpose, has both Latin and Cyrilic)
SKURRI.TTF Skurri (Latin)
SKURRI_CYR.TTF Skurri Cyr (Cyrilic)
The file is 40MB zipped so couldn't upload here, thus I uploaded it on filebeam:
http://filebeam.com/2800653ff8e3eaf7c7866dffff92fbbe
In any case if it's not on topic at least it's now people know not to replace all the files above with one latin font, hehe.