Same thing with Belgian French, much to my dismay.
I speak a language that does this as well (Georgian), where say 54 is ormotsdatotxmeti (two times twenty and fourteen.)
I didn't find maths particularly different difficulty wise, when thinking about it in Georgian or not. What did trip me up, was the times! Up to x:29 it's 29 minutes past x, but at x:30 it is 30 minutes to ++x. Weird.
It survives in part in quite a few other languages as well. E.g. Danish ("fjerds" is a contraction of "four into 20" = 80).
Most other European languages at least (I'm sure it's present elsewhere too, but I don't know enough non-European languages to say) have some remnants of more widespread counting in 12's or 20's or both (e.g. in English a "dozen" is 12, a "gross" is a dozen dozen (144), and a "score" is 20, hence "four score and seven years ago" in Lincolns Gettysburg Address - 87 years).
I speak a language that does this as well (Georgian), where say 54 is ormotsdatotxmeti (two times twenty and fourteen.)
I didn't find maths particularly different difficulty wise, when thinking about it in Georgian or not. What did trip me up, was the times! Up to x:29 it's 29 minutes past x, but at x:30 it is 30 minutes to ++x. Weird.