Los miércoles bebo vino.
Shouldn't the translation be "the Wednesdays i drink wine" (even though it makes no sense) . Because "Los" stands for "The".
The actual translation is given as "on wednesdays i drink wine"
Nothing was omitted, that's just how the phrase in constructed in Spanish. You can't translate it literally word for word. It's like how in English you say, "I am 10 years old." In Spanish it would be "Tengo 10 años." This would literally translate as "I have ten years." (which still conceptually makes sense). Similarly, in this case, the phrasing is different between the two languages.
@Shim Now that i think about i don't think "en" was omitted, but that it could have been there to make the sentence easier to understand. It's like when you use the example "Tengo 10 años," which could as well have been: "Yo tengo 10 años," with exactly the same meaning.