The word Sioux

I would like to clarify something that has always been assumed about the origin of the word Sioux. Everywhere it is discussed about, it is said that it comes from Nadowessiwak, a term by which the Ojibway used to call the Lakota. Then the French shortened it into Nadowessi before becoming Sioux. This I won't contest, but as a French person, and retired French teacher at that, what is incorrect is that you'll read also the way the French pluralize a word is by adding -oux at the end of it. I don't know where this originated, but I can tell you this is wrong. To pluralize a noun in French is by adding an S at the end, just like in English or in Spanish. We do have a few nouns, 7 to be precise, whose singular form ends in -ou, and to which you add an X instead of a S to make the plural. Seven words only! So, with Sioux that would make 8. And why not! The Sioux would become the 8th entry of the list of this exceptional plural form which involved the following words : bijou (íŋyaŋ othéȟika), caillou (íŋyaŋ), chou (waȟpéyutapi), genou (čhaŋkpé), hibou (hiŋháŋ), joujou (wíškate) and pou (héya)! I have no problem with that.
But although I know this is not a discussion about French, and you probably don't care about knowing details of my language, it just bothers me to know that each time someone is looking up the origin of the word Sioux, he/she is given a wrong information.
Waŋná oyás'iŋ slolyáyepi.
But although I know this is not a discussion about French, and you probably don't care about knowing details of my language, it just bothers me to know that each time someone is looking up the origin of the word Sioux, he/she is given a wrong information.
Waŋná oyás'iŋ slolyáyepi.