While in english it’s completely normal thing to say if you’re not sure of a person’s gender.

Well...

You can use "they" without being insulting, as it still presumes personhood, but if you call someone "it" you're dehumanizing them and stripping personhood from them, as "it" is used for objects and things, not people. It sounds like what you're translating would be closer to "it" in English than "them" or "they".