There’s no direct translation:

Mudita is word from Sanskrit and Pali that has no counterpart in English. It means sympathetic or unselfish joy, or joy in the good fortune of others.

Defining mudita, we might consider its opposites. One of those is jealousy. Another is schadenfreude, a word frequently borrowed from German that means taking pleasure in the misfortune of others. Obviously, both of these emotions are marked by selfishness and malice. Cultivating mudita is the antidote to both.

Mudita: the Buddhist Practice of Sympathetic Joy – Barbara O’Brien, buddhism.about.com (undated)

We could all use this but especially writers, right?

Hat tip to buddhism.about.com for the definition but a bow to Swiss Miss for spotting it.