Any living language is a dynamically developing phenomenon. And one of the ways of development is borrowing. If you understand the system and methods of borrowing words, then the meaning of the word "comme il faut" will not be difficult to establish.
In any (especially European) language there are very few primordially exclusively its words and roots, because the
languages of Europe for centuries have closely interacted with each other and with the languages of Asia, Africa, America and Australia (due to colonization).
Foreign tokens can come into the language both to designate new phenomena, and as new names for old phenomena. For example, in many languages there are words (satellite, cranberries, vodka, cabbage soup, borsch, gingerbread and others, calling objects of traditional Russian life). Words that have become international culture are borrowed from Russian. Just as Russian children ask what the meaning of the word “comme il faut” is, the French are perplexed about borsch until they try it.
Borrowings can be of two types. Firstly, there is a more or less accurate phonetic copying of a word and its natural adaptation for a more convenient pronunciation. Secondly, the dismemberment of the components of a word or expression and the translation of parts of the word into the language into which the borrowing takes place. So, more often borrow complex, multi-rooted words or whole expressions. Often, in order to identify such a borrowing, one must have an extensive linguistic outlook or a phenomenal linguistic instinct.
For example, few people realize that the word “Orthodox” is a tracing-paper borrowing of the Greek word “Orthodox”. Over the course of a long history, borrowings from the languages of other nations came to the Russian language.
A brief history of borrowing is as follows: In the X-XII centuries, a lot of Greekisms appeared, that is, roots that came from Greek, especially in the church sphere. In the XII-XIV centuries, Turkisms came: the Mongol yoke could not pass without a trace for the language.
Next - the time of Troubles, Cossack riots, the split - and close interaction with the Commonwealth. In Russian, polonisms arise - that is, borrowings from the Polish language. Then, of course, the meaning of the word "comme il faut" was not yet known.
Peter I was very fond of Dutch and German culture, and this also did not go unnoticed by the Russian language, having echoed a number of Germanisms, especially in the military and shipbuilding spheres.
In the second half of the 18th and 19th centuries, as you know, everyone was crazy about France and all French culture in general. The meaning of the word "comme il faut" was then known to any child: "good form, rules of decency." Translated from French, the phrase "comme il faut" means "as needed." Gallicisms did not keep themselves waiting and occupied many areas of life - military, court, art, fashion.
Sometimes we do not even see gallicisms in our native language: battalion, boa, marmalade, tights, broth, comme il faut. The importance of gallicisms for the Russian language is difficult to exaggerate. They undoubtedly enriched our language with a variety of sound combinations. But now, unfortunately, many people have begun to forget the meaning of certain borrowings, and this is
not comme il faut! The meaning of the word is the smallest thing you need to know about it.
Well, the 20th century is famous for Anglicisms and Americanisms. They came along with jeans and McDonalds fashion, appeared along with thin models and iPhones, sailed from overseas along with rock culture and dollars.
Undoubtedly, the 21st century, the first century of the new millennium, will also bring us new phenomena and invariably new borrowings.