It has not any meaning. It is just an introduction to a question. In English you move predicate to the beginning: You are a girl. -> Are you a girl? In Polish you just add "czy", so: Jesteś dziewczynką. -> Czy jesteś dziewczynką? :)
By the way, you can skip the word "czy" if you speak in informal language. But then, you must accent that it is the question.
It's ĉu in Esperanto.
Vi estas knabino. You are a girl.
Ĉu vi estas knabino? Are you a girl?
What does Esperanto, a useless man-made language, have to do with Polish for English-speakers?
Some people might find the similarity interesting and useful. The language was created and initially developed by a Polish speaker. Some of us here have studied both languages, and every opportunity to compare langauges can help reinforce learning. Even when I'm studying a language with English as the interface language, I'm thinking about examples from all sorts of languages that can help reinforce concepts that are significantly different from English: like, thinking in English is pretty much useless to me for trying to wrap my head around cases, so I think of examples from German and Finnish when studying Polish, Russian, Ukrainian, Lithuanian, etc. I'd use Latin for the same purpose, too, but haven't learned enough of it yet. No language is useless when it comes to learning languages.
The fact that natural languages develop chaotically may make them beautiful and interesting, but it's also their biggest flaw.
Reminds me of ですか in Japanese, which is commonly used to turn a statement into a question. Except that ですか is added to the end of a sentence rather than the beginning.
Rather than ですか, I'd say czy is more comparable to just か, since the です part of ですか is the copula (to be) and the か part is what makes it a question. Though the difference is that, from what I understand, czy is only oned for yes/no quetions, while か is used for any question.
Technically, it translates to "is it the case that...." That's the beauty of czy: it expresses something that's awkward and lengthy in Germanic and Romantic languages in a very efficient and sensible way.
"Is you is, or is you ain't my baby?" Hahaha! Just kidding. Czy jesteś... is like "'Are you are' a girl?" or "Do you be a girl?" If I'm being literal, that is.
One of the easiest ways I've found to understand this word is to translate it as "whether," or even "if." It's sort of like saying, "Whether you are a girl (or not)?" This will help you in the future, when czy may be followed by more than one option.
Of course, that's not to say you should translate it as "whether." :-) It may help you to use that meaning to parse the sentence in your mind, and then come up with the best (and simplest) translation for it on a case-by-case basis.
I'm not protesting, as you seem like you know what you're doing, but I have to say that I don't understand this analogy... "czy" makes it clear that it's a real yes/no question, how is 'whether' similar?
I would translate "czy" as 2tell me whether .Certainly I advise this option for beginners in Esperanto to translate "Cu".
What you should have asked is "Czy jesteś dziewczyną?" because dziewczynka means small girl, female child.
Li was used in old Polish texts the same way you showed it is in Serbo-Croatian. Nowadays it is considered obsolete and aside poetry not understood.
Możeszli mi pomóc?
Znaszli ten kraj?
In Russian it's similar. Li following a verb is a short form of [verb] ili niet?, "[verb] or not?"
Yo I wrote "you are a girl" it is like the same thing and even direct translation would be more correct, especially if formal, "czy" come on currentlsyons.
If the Polish sentence used "czy", it definitely is a question and thus only "Are you a girl?" can be accepted.
If the Polish question was just "Jesteś dziewczynką?", then "You are a girl?" could be accepted, because it could be someone being surprised that you're a girl.