>>37749127I can’t speak for Japanese, but I do know Chinese and kanji are taken directly from there.
Mouse and rat are called 老鼠(laoshu). The same thing, and cyndaquil is called the mouse Pokémon. B-but cyndaquil is an echidna! Ok cool, the Chinese characters for echidna are 针鼹(zhenyan) and what do you see in that second character? 鼠 the same character as in rat/mouse. And the entire name means a spikey anteater.
Now, Fennekin. Sure you can say Fennekin is a Fox sure. But what is the Chinese word for a Fox? 狐狸(huli), which the first character is Fox, the second character means raccoon dog or a Fox like creature. So we can find that culturally speaking rats, mice, echidna, anteaters, are the same thing hence cyndaquil is a rat. And we can’t find that in the cultural heritage of Japan a Fox, dog, and raccoon would be considered similar enough to be the dog in the Chinese zodiac.