I've never come across "cris" personally. It wouldn't make the same sound.
but when we are asked to translate belt it is "cris"
I have never heard the word *cris and nor has my dictionary. It might have been a typo that has now been corrected.
Why crios instead of cris?
Crios is the 'correct' spelling, but it is not a word I grew up with in a solidly vernacular Gaelic community.
I would be interested to know what word you did use.
I think I used cris but don't even remember why I thought that was correct.