Funnily enough, I have the opposite, I moved to Portugal with a Brazilian partner. I am slowly reading fiction books in Portuguese (which I study/work in), while my main reading language is English.

I read in small chunks and give myself plenty of time to reread if I need to, I prefer paperbacks because I'm really bad with e-books as I can't keep my attention glued to the screen. But the dictionary idea is what I do, just manually typing into google translate or look for the definition online.

I'd say read in small chunks, if you feel getting tired and let's say you read x pages, that's good for starters, even if you read 2 pages a day, it's good. It comes with forming a habit and getting your brain used to the language. I also like to keep coffee next with me and remember that you reading in a different language, is factually badass, so small encouragements help too!