Here are some ideas:
* Fairy languages: In many stories, fairies have their own languages, often described as musical, melodic, or even unintelligible to humans.
* Elvish languages: In Tolkien's works, Elves speak languages like Sindarin and Quenya. These languages are complex and beautiful, often used to portray a sense of ancient wisdom and magic.
* A made-up language: Writers can create their own languages for their fictional creatures, adding to the unique world-building.
Ultimately, the language a pixie speaks depends on the specific story and the author's creative vision.