We don’t have any limitations on languages for the titles we print and distribute via print-on-demand. However, there can be issues with our partners ingesting metadata for non-Latin character languages. For those, please provide the metadata transliterated. For example, when providing metadata for the Russian language edition of "War and Peace" we'd want the title in the Latin alphabet as "Vojna I Mir" not as "Война и миръ" in Cyrillic.
For languages that read right to left, you’ll also want to alert us before approving your proofs, so that we can manually intervene to create the correct cover jpeg.