As an ordinary user, it is currently impossible to name a costume using the writing system of other languages. Take for example Chinese:
(Yes, the limitation still exists when you set your language to Chinese.)
This is terrible for anyone who speaks any language other than English as these users won’t have the foggiest idea what they’re naming their costume, either inputting random characters or needing a translator of some kind. You can set nearly anything customization-wise in Roblox to whatever language you like (barring your Username, for example) yet costumes don’t have the same freedoms, only allowing alphanumeric input.
If Roblox is able to address this issue, it would improve my, and others’ experiences because non-English users would able to name their costumes in their native language.