I'm Swedish, and I do all my comics in English!
I don't have anyone else proof-read my comics, but I do proof-read them multiple times myself, just to find spelling mistakes and grammar-errors. A few slip past me, but I mostly manage to deliver mistake-free pages!
I think it's partly correctly rendering idioms, and part of it is cultural differences. Some things are perfectly okay and normal in everyday speech in Swedish that would be considered strange or rude in English, for example. Swearing, for example; it's 100% okay to swear on Swedish tv in ways that would get bleeped on American tv, for example. And we rarely use sir/ma'am/miss to address people, and rarely refer to anyone as our equivalent of Mr [surname]/Mrs [surname] (it would be Herr [surname]/Fru [surname] or Fröken [surname] when addressing a younger woman).
Using people's first names even if you don't know them personally is normal here - I understand that it isn't elsewhere. If you meet someone named Anders Svensson, you're not going to call him Herr Svensson, you're going to call him Anders, because that's his name. Like, the only people I know off the top of my head that normally get addressed by their title is, like, the Prime Minister and his cabinet and, like, members of the royal family? And even then I've heard journalists address the crown princess as "you" in tv-interviews?
So little things like that - modes of address in everyday speech, what level of swearing is or is not acceptable, etc., - are things that occasionally make me stumble. But I mostly get by okay - to the point where I've had Americans assume I'm an American expat who just happens to live in Sweden.
But I am, in fact, a 100% homegrown Swede.
