BUR #5373 has been approved by @evazion.
create alias shinku_izumi -> cinque_izumi
シンク Cinque is meant to be a British/Italian name, like most of the names in the series.
The source of the official English name is apparently the official English translation of all three seasons of the anime, the LN, and the manga. I wasn't able to find any official Japanese media that featured a romanization.
Compare Cinque (Nanoha) (チンク Chinku, or Shinku).
It's worth noting that Shinku could also have a double meaning as 真紅 shinku (crimson / scarlet), and that Cinque's family name Izumi is Japanese, unlike all the other characters with English given names; see Dog Days for a list.
Updated by LQ