I've run across a variety of situations both personally and on discussion threads where seemingly normal systems will suddenly start showing odd behavior, including slow application launch times, extensive login times, or just specific functions of a program (ie, menu access) not working. Many times bizarre system behaviors such as these in addition to obvious problems such as distorted or garbled text may be nothing more than a problem with fonts; however, tackling font problems can be one of the most tedious and frustrating ventures in OS X.
There are several approaches to managing fonts, some that are crude (ie, "remove them all and start over") and others that take a long time, depending on the task. One problem with troubleshooting fonts is that it's a fine balancing act. While the presence of some fonts is required for certain application or system features, those can conflict with other fonts that are required for other features. As such, if you remove the wrong one you can solve one issue but introduce another.
Global font management has been desired for years, and while there have been advances, no solution encompasses everything. This is mainly because companies that develop applications which extensively use fonts tend to use their own font organization techniques (ie, storage locations). Other times a company will require a certain type of font and not adopt newer technologies, requiring you to have multiple font formats on your system, sometimes keeping them in global locations where other program may have trouble when trying to load them. The possibilities go on and on.
Apple has done a decent effort in tackling font issues by introducing Font Book, which contains font validation routines to isolate a number of problems that may crop up with Fonts. However, Font Book is still limited in what it can detect, and even when fonts are found to be valid there still may be problems.
For an extensive look at font management and handling font problems in OS X, the following tutorial and FAQ by Kurt Lang is an excellent resource for anyone, but especially for those who extensively use fonts: http://www.jklstudios.com/misc/osxfonts.html
Kurt Lang's article is well organized, but also long so if you are just experiencing problems with fonts, here are some basic troubleshooting steps to take:
Run validations with Font Book
Launch Font Book and press command-A to select all fonts. Then from the "File" menu select "Validate Fonts" and wait for the results in the font validation window. Keep in mind that even though you may find minor problems with your current fonts, its best to follow the saying "if it's not broken then don't fix it", and leave well-enough alone unless you're experiencing problems.
Clear the font cache
In OS X, fonts are handled by the Apple Type Server process, which stores commonly used fonts in a cache for quick access. If there is corruption in this cache then you may experience a variety of troubles. To clear the cache, in pre-Leopard versions of OS X go to the /Macintosh HD/Library/Caches/ folder and remove the "com.apple.ATS" file. After doing this, restart the system.
For OS X 10.5 and later, you cannot easily access the user and global font caches, but you can use Apple's "atsutil" terminal command to manage the ATS process. Open "Terminal" and enter the following commands to clear the user (or global) databases and restart the server:
atsutil databases -removeUser
atsutil server -shutdown
atsutil server -ping
NOTE: Use "sudo atsutil databases -remove" instead of the first command to remove the database for all users.
Avoid older font formats
If you can, avoid ".dfont" and "Type 1 PostScript" fonts. This suggestion may depend on the requirements for various programs, but if you have an older font suite that you are thinking about installing, it may run into problems with newer programs so you might consider getting an updated version of the suite before installing. Granted you can always try, but there is the potential that older font formats can cause problems so we recommend you stick to the more modern ".ttf" and ".ttc" fonts.
Manually clear out duplicates
Font Book has an option to "Resolve Duplicates" (available in the "Edit" menu), but this is limited in functionality and may not remove the specific font duplicate which you desire to remove. As such, the best approach to managing duplicate fonts is to do it manually (tedious, but effective if done correctly). In Font Book, you can use the "Show Font info" option (command-I) to see information about a selected font, and especially where the font is located on your system. Doing this for your duplicate fonts will allow you to select which one to remove, either by removing it from its font folder, or by right-clicking it and selecting "Disable".