Back up all data.
Launch the Font Book application and validate all fonts. You must select the fonts in order to validate them. See the built-in help and the support article linked below for instructions. If Font Book finds any issues, resolve them, then boot in safe mode* (by holding down the shift key at the startup chime) to rebuild the font caches. Boot again as usual and test.
Mac 101: Font Book
*Note: If FileVault is enabled under OS X 10.7 or later, or if a firmware password is set, you can’t boot in safe mode. In that case, after running Font Book, launch the Terminal applicationin any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Terminal in the page that opens.
Drag or copy — do not type — the following line into the Terminal window, then press return:
sudo atsutil databases -remove
You'll be prompted for your login password, which won't be displayed when you type it. You may get a one-time warning not to screw up. After running the command, reboot as usual.
