It is probably Apple system font problem. How to reproduce/check? Open "Font Book", select all fonts, then Arial, then Normal. Result: There is no font preview on the right pane of Font Book. When you select other font style (i.e. Italic) preview is visible. I've tried restoring original fonts (from File menu) but Arial/Normal is still missing. Same with Calibri, but in this case there is no Calibri on the list!

OK, I've found the reason (and temporary solution!). It's because of LCD Font Smoothing enabled (CGFontRenderingFontSmoothingDisabled option in terminal) If you have Arial problems check current settings (it will be 0): defaults read -g CGFontRenderingFontSmoothingDisabled 2. To repair disable setting (set to 1) defaults write -g CGFontRenderingFontSmoothingDisabled -bool YES Then restart applications with font problems and voila, Arial is visible now.