[chr1]

True, sound changes like dvesti÷trista÷semsot make learning harder, but i'd say that's not really the property of the number system but of a language as a whole, since similar shifts are present in other places too.

For me Russian numbers were simpler than French because you could learn the basic idea quickly, and then pick up subtle sound shifts by watching tv/reading.

(disclaimer, i am not a native speaker but learned Russian at school age so may be misgudging the difficulty of the language)