"In the lift are green walls" ...that's not grammatically correct English
A note from a native Russian: That translation will be correct if there is a major pitch fall on "в лифте". If the pitch fall is on "зелёные", then the sentence means "The walls in the elevator are green". It the pitch fall is on стены, then it means "It is the walls of the elevator that are green". If the pitch fall is evenly spread throuhgout the sentence (neutral intonation), then the best translation will be "The elevator has green walls".
Isn't the grammatical correct translation of the elevator has green walls "у лифте есть зелёные стены" ?
It's not. "У лифте" is grammatically incorrect. Did you mean "в лифте" or "у лифта"?
In general, we use "есть" when we need to establish the existence of something. You don't need to establish the existence of the walls in the elevator. You know it has walls. We are talking about their color, not the fact that they exist.
"В лифте есть зелёные стены" means "there are green walls in the elevator". I am not sure about the context.
"У лифта есть зелёные стены" technically means "the elevator has green walls", but it sounds weird. The only context for it I can imagine is when a parent is explaining an elevator to their two ears old. "Что есть у лифта?" - "у лифта есть зелёные стены!" - "правильно, Сашенька, молодец! А ещё что есть у лифта?" - "у лифта есть двери!"
Yes, I always find myself translating sentences this way and I always get them wrong. I'll keep reporting it wherever I see it because it is technically correct! No matter how "weird" someone thinks it sounds.
For whatever reason a lot of people disagree with us. It may sound a little old fashioned but all of the necessary info is there. It is faster and more efficient to translate it this way. That way I don't have to go through the step of flipping the subject and the predicate.
It is fine to say that in English. I don't know if it is likely to have the same emphasis as the Russian sentences they are giving us or not.
Omitting "there" I might raise my voice on any of the words to draw emphasis that this part is contrary to expectation (eg. "in the TRAIN are uncomfortable seats" because my friend has just asserted that it is the TRAIN STATION that has uncomfortable seats and I am correcting them). This way the emphasis is not on the seats' EXISTENCE but on the part you are giving emphasis to.
Or if I leave out "there" I may be giving a list and the emphasis is either the sum of what I'm saying or not until the end: I'm giving you background information. (eg. In the train are uncomfortable seats. Weird people talk to themselves. The floors are dirty. I HATE THE TRAIN.)
You can do these emphasis shifts equally well with "there" included. You HAVE to include "there" for your listener to understand you just want to point out the existence of the seats.
I believe you meant "it is green walls in the elevator", which is indeed close but doesn't make sense in English since you are wanting to make a standalone statement.
You may be getting this confused because we do have sentences like "it is cold in the elevator", "it is dark in the elevator", and "it is loud in the elevator". You may notice "cold", "dark", and "loud" are actually describing a property of the environment inside the elevator. When you say "it is green walls in the elevator", you are really saying that the environment inside the elevator is "green walls".
Here we are wanting to describe a property of the elevator so we say "the elevator has green walls".
There are rare cases where you would say "it is green walls in the elevator". Here's one example - Boy: "Is it green walls in the elevator and blue in the bathroom, or blue walls in the elevator and green in the bathroom?" Girl: "It is green walls in the elevator."
The reason why that works is because it is answering a "either...or" question.
Just a small correction to your fantastic and in depth comment, @Nemesis105666 - the correct English would be "Are there green walls in the elevator and blue in the bathroom?" to which the correct answer would be "There are green walls in the elevator". - Because "walls" is plural and we're using there to say something that is "in the elevator", rather than something that the elevator is. :)