The plugin interface has a weird font, it’s gibberish!

If your Animation Composer plug-in interface looks this:

It looks like you’ve somehow corrupted the Lucida Grande font. You probably have multiple versions of the font installed.
Open the Font Book application and check there is no yellow exclamation mark sign next to the Lucida Grande font.
 

Here’s a screenshot so you can see how it should look when there are no issues with the font.