This question already has an answer here:
I saw somebody with a
Python gold badge but can't dig up where now... This badge isn't listed on Stack Overflow (http://stackoverflow.com/badges). Where is the reference?
It's in the "tags" tab of the badges page.
Look in the upper right part of the page, just below "Ask Question"; there you'll see the two tabs, "general" and "tags". Now imagine a circle around "tags".
(When they added the tabs, it took me at least a month to notice them.)