We do require that all projects also include an English version of their description, rewards, and other key elements. You're welcome to include translations in other languages as well, however. Kickstarter is a global community, and including translations will definitely help your project have a wider appeal.
If you include text or audio in a language outside of those that we currently support (English, French, German, Spanish, and Japanese), we also ask that you include English translations or subtitles.
Interested in including another language on your project page? Check out our Best Practices for Bilingual Projects.