In Apple’s Font Book, you can click the All Fonts collection, followed by clicking a font and then pressing Command-A to select all fonts on the system.
Then choose “Validate Fonts” from the File menu, and the program will check for conflicts, compatibility, and damage to your fonts.
In all cases, from the validation window you can click the checkbox next to a font to select it, and then click “Remove Checked” to delete the selected fonts.
Unfortunately doing things this way can be a bit of a burden, but is the only way to approach this manually.
It may help to put the Font folder in list view, and then sort the list by “Date Added,” which will categorize the items in it by when they were placed in this folder.
For older and incompatible fonts, the system will usually just not load them; however, there may be instances where it tries and results in a persistent error, slow loading, or some other odd behavior either with the system or with the specific program you are using, that can frustrate your workflow.
Expanding the font with the error shows the only problem here is a duplicated font file.
Fonts are not just files, but rather system plug-ins, similar in ways to an extension or add-on application.
When added and activated, they load into memory and are associated to programs by the system so programs can make use of them and show information about them.
In the case of damaged fonts, the system may attempt to load them and either not be able to and result in a hang or crash, or will load them and you will see corrupt symbols appear instead of the desired font face.
At other times, the symptoms may not be so apparent, such as a fault with only specific characters that cause problems when they are displayed.
While you can usually get away with minor errors found in the font validation routine (noted by a yellow circle with an exclamation point in it), you might want to investigate the cause for this problem.
If you see any errors that are colored red, then this indicates a problem that will likely cause a disruption to programs and services that use this font, and you should consider disabling, removing, or reinstalling the font.
These take precedence over other fonts; however, a program can install a font in the global font folder that is the same as one in the system’s font folder, and result in a font conflict.