so you mean Co=what to=is and jest=it.
wrong:
co = what
to = this/it
jest = is
And the word "Czy" (in this context). How do i translate it.
Use inversion instead
Staef, is your mother tongue Swedish?
Staef, czy twoim językiem ojczystym jest szwedzki?
(btw, "ojczysty" comes from the word "ojczyzna" = homeland, which comes from the word "ojciec" = father, so don't get confused that ojciec = mother :) it's not
like in that example, you use "czy" in questions that in Swedish/English have the inversion of predicate (verb)/subject (noun or pronoun)
(and no words like: what - "co", where - "gdzie", who - "kto"), those are the questions that can be answered with a simple yes/no. In English they are corresponding also to question where in Simple Tense you use do/did at the beginning. Inversion in Polish isn't a grammatical tool, it my be used beacues of the style, but it doesn't change the meaning itself.
examples in English + Norwegian and then Polish
Is it a new car? Er det en ny bil? Czy to jest nowy samochód?
Do you speak Polish? Snakker du polsk? Czy mówisz po polsku? (or better "Czy znasz polski?")
there's also other other use of the word "czy": in composed sentences, where the second part is normally a yes/no question
I don't know
if/whether she comes today.
Jeg vet ikke
om hun kommer idag.
(Ja) nie wiem,
czy ona dzisiaj przyjdzie.