Unicode characters, such as ♥ and ♡, cannot be used. All emojis work, though! However, we must use our own emoji library, as your device's library is copyrighted, and we don't want any trouble ;)
Some languages are not supported at the moment, such as Hangul, Han, Cyrillic, etc. However, we are working on implementing them in the future. If you encounter any issues or the result is not what you expected, please don't hesitate to contact us.