You can add emojis but to be sure that they'll come out fine once printed, you can refer to the following link to double check: Find your emoji 👈
NB: The ♡ emoji turns into a ❤ and will appear as ❤️ in your creation.
Regarding the cyrillic and the asian alphabets, we're having trouble printing some of their letters and therefore invite you not to use them throughout your creation to avoid any disappointment.