Omnilingualism

Omnilingualism is the ability to understand and speak any language without training in it.

Whitelighters have this power to a degree, wherein they can speak any language their charges speak. In 2001, Leo Wyatt did not speak French fluently, and was practicing for his and Pipers honeymoon to Paris. Later in 2002, he had a charge in Paris and was capable of speaking fluent French. When Wyatt switched Piper and Leo's powers, Piper was able to speak fluent French, which came as quite a surprise to her. ("Exit Strategy," "Siren Song")

Leo was able to speak Arabic, where Phoebe and half-whitelighter Chris couldn't to read the warning on a genie's bottle. ("I Dream of Phoebe")
 * This may mean Leo has a charge that speak Arabic, or perhaps he just needed to understand it for the situation.

Paige could speak Maori to speak to her New Zealand charge. ("Imaginary Fiends")