In the early 1990s, video game characters were often dubbed by the developers and their colleagues, and SFII was no exception. Where the game differs from some of its competitors is that a given character may have been dubbed by more than one person. Akiman, who was involved in the recording of the lines, wanted as many people as possible to participate, even if the lines of some people were left. The voices weren't very clear on CPS1, so it was possible to do this without the players noticing.
Thus, Chun-Li was dubbed by 3 Capcom employees: the Spinning Bird Kick line was spoken by Eri Nakamura, the graphic designer in charge of Honda, while a background designer did her victory cry ("Kyahahaha! Yattaaa") and a third person recorded another line.
Regarding Ryu and Ken (who share the same voice in the first iterations of SFII), the graphic designer in charge of Guile lent his voice for the Hadoken and Shoryuken while the one in charge of Boxer did the Tatsumaki senpukyaku. The "Cho" pronounced by Claw during his Flying Barcelona attack was recorded by Dany (who animated Iceman from X-Men Children of the Atom and Roll from Marvel Vs Capcom 2).
The announcer was Mr. ゴル (Gol / Gor / Goru), a foreigner originally introduced by a former classmate and collaborator of Capcom president Tsujimoto. It seems that Akiman called him because he was the only foreigner present at the time. He recorded his voice for the country announcements, but when more words had to be recorded, he was no longer available and Mr. Scott, a programmer, was called in.
According to Eri Nakamura, lines had to be re-recorded faster for the Super NES version because of the limited cartridge size.
From the CPS2 (Darkstalkers, Street Fighter Alpha, X-Men COTA), the sound quality was higher so Capcom hired professional voice actors.
Sources:
Akiman's recording policy
https://twitter.com/akiman7/status/1326153629603033088
Ryu and Ken
https://twitter.com/gilmanhouse/status/1326158981463633920
https://www.otaquest.com/yoko-shimomura-interview/
Flying Barcelona Attack
https://twitter.com/gilmanhouse/status/1326154536583536640
https://twitter.com/gilmanhouse/status/1326240483698356225
Chun-Li
https://twitter.com/KIMOKIMO_Club/status/1326147894630494210
How to make Capcom fighting characters
Narrator
https://twitter.com/ryo_redcyclone/status/1325997842238877696
https://twitter.com/sjxqr393/status/1325999852577157122
https://twitter.com/akiman7/status/1326157042088701956
SFC version
https://twitter.com/KIMOKIMO_Club/status/1326151416428154880