It's the problem wth trying to translate things phonetically. Characters don't exactly sound the same as characters in the other language so it's written as close as it can get which leads to misunderstandings.
The "official" phonetics of the English version of the word are "(t)so͞oˈnämē"
Brackets mean it's an optional bit to pronounce so tsu-na-me and su-na-me are both right in the eyes of the linguistic people at Webster.
Brackets mean it's an optional bit to pronounce so tsu-na-me and su-na-me are both right in the eyes of the linguistic people at Webster.