Ask HN: For expats living in Europe: how hard it is to progress in your career?
For example, if you're working in a country where you don't have fluency in the local language, is this a barrier?
You need to learn the language. You don't have to master it, but you should be able to make conversation. You should be able to talk in sentences and be comfortable (at a restaurant, at a bank). The rest will come as you immerse yourself.
The only clear exception to that rule is banking. I have traveled extensively and when I do banking they always want to do it in English. I know a number of island languages, but banks have instructed the people where I live to talk in English only.
Hope that helps.