Medium has 2 meanings: 1) Medium: Average / not big not small but in between The size of the shirt is medium 2) Medium: A channel / port / Third party / Agent (between two things) If your native language is Arabic but you speak English well and you want to learn Japanese from a Japanese person, he will most likely speak to you in English. Therefore English acts as a "medium".

The sentence is grammatical but it doesn't make any real sense. You can use the word "medium" (noun) as a more formal synonym for "way". e.g. The English language is the medium through which many people worldwide do business.

I'm not a speaker, I can't be sure. But fo me it sounds somewhat like "la langue de moyen" or even "la langue moyenne" would sound in French - that is not good at all:) Cf.: "English is the medium of instruction...." (about schools where students are taught in English) - you see, here 'medium' is used in a way similar to 'moyen'. "English-medium education" (e.g. https://en.wikipedia.org/wiki/English-medium_education) is another wording familiar to me. Here "english-medium" acts as an adjective: Education, where English is the medium.

KP, you're right, no native speaker would ever write it that way. As Michael said, we can understand what the intention behind the sentence is but it is poorly written.