doesn't "it's lemon" refer to lemon taste, or colour, or being made from lemon etc?
"to jest cytrynowe" or "jest cytrynowy/cytrynowa/cytrynowe" would be used then.
Is the article 'the' or 'a' truly necessary here? If someone asked "what flavor is this?" You would answer "It is lemon" not "it is a lemon". Therefore shouldn't "This is lemon" be accepted?
As I wrote in the comment which is currently just above yours:
"True, but the Polish sentence doesn't talk about a colour nor a flavour. Well, maybe it could be about flavour, but it would be rather a colloquial construction then."
I guess the most probable answer would be by just using one word, the adjectival form of lemon: "cytrynowy" (or its form, whatever matches the noun that is described).
You can also say: To (jest) cytrynowy zapach (scent); To ma zapach cytryny (has scent of a lemon); o smaku cytrynowym ('of lemon flavour'), things like that.
Ah. So the easiest way from the looks of it is just to use more words to establish context. Thanks!
This is lemon is also correct English e.g. if you are taking about a colour or flavour.
True, but the Polish sentence doesn't talk about a colour nor a flavour. Well, maybe it could be about flavour, but it would be rather a colloquial construction then.