After having lived and worked in multiple EU countries, I'm convinced that language is the single biggest barrier to true freedom of movement of workers in the EU. In Germany, for example, you cannot assume any daily task can be accomplished without the German language. You're then faced with either constantly dealing with communication problems with everything in your life, or paying the significant opportunity cost of learning a new language -- which you will likely never learn to high enough degree to fluently use in business, and which won't help you in the next country in which you live.
What is needed is a joint common language (English) that everyone in the EU learns starting in kindergarten and in which you're guaranteed state services in every member state. But there is no chance the French and German speakers would ever agree to that, it is like a religious issue.