You can use online language dictionaries like WordReference.com. You can also find pictures like this one on the Internet :

There is another one great picture and I will edit this answer if I find it.

BONUS : searching the previous picture I found this web page : http://www.babelcoach.net/fr/vocabulaire_anglais/vocabulaire_injures_et_insultes

The Wiktionnaire has some categories that might be interesting in this case and they have their counterparts in the Wiktionary.

• Termes péjoratifs (pejoratives)
• Insultes (offensive terms)
• Termes vulgaires (vulgarities)

the French ones are quite extensive, perhaps too much, and the English ones are not perfectly accurate and somewhat small, but between them, you should have enough material to swear better¹ than a native speaker.

_{1. Or worse, depending on your point of view.}