In my WIP ("progress", heh) there is a Dutch dentist and I'd love to move the setting to Germany - no researching breakfast food, no researching taxes, no researching: houses bought or rent? - but it is impossible for me to imagine him as German! So I have to go through with it.
Couldn't you have your Dutch dentist move to Germany? Like, set the story in Germany, but keep the dentist as he is? There's loads of people living in countries that aren't their country-of-origin.
To the OP: I'm in the US, but I set most of my (almost-done WIP) sci-fi/time-travel/romance novel in modern-day London. Although, I sort of cheated and made the female MC a displaced Bostonian from 600 years in the future, while the male MC is a displaced Canadian from 700 years in the future. So if they get certain things wrong, it's okay. Their friends and co-workers are British, so the female MC gets corrected occasionally for calling a torch a flashlight, stuff like that. (I don't necessarily recommend this approach, however, as I also had to invent two entirely new cultures for when they were each at home, in the vaguely post-apocalyptic future, instead of time-traveling. The jury's still out on whether I did that successfully or not.)
On getting it right: it definitely helps to immerse yourself in the culture. I've watched (and written) Doctor Who, Torchwood, and Sherlock for years, which helped with getting the basics right. Visiting London a couple of times made a difference. Having British beta-readers is very important. They can catch tiny (or not so tiny) details that you've overlooked. Google maps (esp. street view) can help tremendously if you can't make a trip to the UK. Also, reading tourist guide books can provide unexpected info, like whether you're supposed to tip at a restaurant, or the best way to get from one place to another. I also read a lot of websites that translate British words and phrases.
It's funny how things suddenly make sense once you learn the lingo. When I was a kid, I watched the miniseries "Hitchhiker's Guide to the Galaxy" over and over, but I didn't have a clue about British culture or language. So when, as an adult, I learned what "zebra crossings" were, I suddenly understood the part in the show where (paraphrasing from memory here) mankind proves that God exists, but the whole point of God is that you can't prove he exists, so it causes a paradox that literally changes everything, so white becomes black/black becomes white, and everyone gets killed at the next zebra crossing. (Previously, I thought it must be some bizarre reference to zebras stampeding across the road in Africa. . . .)
It's also funny how I now (unintentionally) use British phrases and words in everyday life. It confuses my friends and family.