Honestly, I believe some of the comments that might occur could be anecdotal.
Certainly, writing scientifically in a language that is not your mother tongue.... Even now, after 30 years, it's harder for me to write in French than in English, but I do it all the time. It is hard to write. I think you need some extra help to write in a different language. Certainly, for anglophones writing in French, it's a lot harder. You need some help to be concise. Scientific writing is ultraconcise. Our grant applications are very small, so you're always asked to keep things trim. You need help.
I'm not sure if I answered appropriately, but, yes, it's hard. From one language to the other, it's hard. It's hard for me to write science applications in English and, probably, hard in French for people with French.