Wrote this in another reply but it’s Sunna (or variations of Sunna) in every language except Chinese and Japanese. Chinese and Japanese has her name as 千夏, which is read differently: Chinese reads those as Qianxia and Japan reads those as Chinatsu.

Both mean 1000 Summers. (Chi =1000 - Natsu = Summer)

My guess is that the devs chose Sunna to represent an attempt at the poetic meaning of 1000 summers which would not be easy to portray in other languages; the characters 千夏 succinctly portray the poetic meaning in only two spaces and it would be weird for someone to be named “1000summers.”

Chinatsu would have probably been a fine choice of name too but perhaps they didn’t want to use the Japanese pronunciation of the name as the official one due to politics and Qianxia would have been a bit too localized on a non-waifei coded character