That's nothing compared with the bonkers things that happen when you use numerals in Russian.
1 book - odna kniga (nominative singular, as you'd expect).
2 books - dva knigi (genitive singular).
3, 4 also genitive singular. Singular, right? OK. Now
5 books - pyat' knig. Genitive plural.
6 up to 20 - genitive plural.
21 books - dvadtsat' odna kniga, nominative singular.
22 - 24, genitive singular. 25 - 30, genitive plural. Similar pattern from then on.
In Chinese and Japanese you have to use a classifier to link the numeral to the noun. It's as if you were to say 'six head of cattle', but a similar construction for every noun and you have different classifiers for different nouns.