how do we say first, instead of one? birinci?
yes, birinci. But we don't use ordinal numbers (birinci) when we talk about dates
Why is Bugün bir nisandır wrong? Would it mean Today is an april?
That would have been my choice of wording as well. Without the "dır", though. You don't need it in this context. "Bugün 1 nisan" is accepted.
Nope, that is not used in Turkish :)
Do people in Turkey 'celebrate' April 1st? Or is there something similar? :)
Not really, but it is becoming more and more known.
Thanks for the answer and for the article! :)