Looking at the raws, he does use english on page 19. So it's an understandable choice for the translator to use romanji.
ここは任せてもらってもノープロブレム(no problem)!
ユー(you)は早く行っちゃいな!
Then he uses ナーシング, nothing, several times and I'm not typing all that out.
Also, dem Street Fighter references lol.