It depends on which language version you were watching.
In the English dub version on Netflix in the UK, Karum (voiced by Bambadjan Bamba) speaks plain English with a slightly dodgy Nigerian accent.
However, in the original Korean language version Karum is voiced by the actual actor (Nas Brown) and is speaking in Nigerian Pidgin (a creole language loosely based in English).
However, I can find no official confirmation of this anywhere, so I decided to get creative, and check the Korean subtitles when Karum speaks, and as luck would have it, it WORKED!
At approx 1hr 20mins in, we have a scene where Karum is offcamera and speaks these words in the English dub:
Since when am I in charge of the money?
And the Korean subtitles give this (via Google translate):
in pidgin, nigeria
Have I been in charge of money ever since?