English is, as far as I’ve heard, one of the hardest languages to learn due to inconsistencies. It’s a godawful mashup of Germanic, French, and Latin bases with a large smattering of random other languages. (There are neat charts on this wiki page.)
Japanese is similar but not quite as bad. It’s a Japanese/Chinese primary mix with some English influence (mostly katakana words) and a small smattering of other things (as any language will have). But it has only two main bases, and we thankfully don’t have to worry about Chinese tones.
Not sure, but this may help you feel better about having to learn the exceptions due to the counting system…
Cardinal numbering in English follows two models, Germanic and Italic. The basic numbers are zero through ten. The numbers eleven through nineteen follow native Germanic style, as do twenty, thirty, forty, fifty, sixty, seventy, eighty, and ninety.
Standard English, especially in very conservative formal contexts, continued to use native Germanic style as late as World War I for intermediate numbers greater than 20, viz., “one-and-twenty,” “five-and-thirty,” “seven-and-ninety,” and so. But with the advent of the Industrial Revolution, the Latin tradition of counting as “twenty-one,” “thirty-five,” “ninety-seven,” etc., which is easier to say and was already common in non-standard regional dialects, gradually replaced the traditional Germanic style to become the dominant style by the end of nineteenth century.
See? We have weird mixed-up numbers too!
Edit: I guess LucasDesu pointed out the English numbering inconsistencies before I did, and more concisely to boot. Whoops!