No, there are no restrictions.
For a start, some art forms such as mime, instrumental music and dance are inherently non-verbal.
Then an Italian opera is going to be in the Italian language. Ditto French, German, Russian, Chinese opera.
We’d love to have indigenous art forms in their native languages.
Finally we aim to be a truly international festival and welcome events in any language their performers wish to present them. That said, we really don’t know how to make the directory friendly for non-English speakers but are prepared to try.