In the USA most of us have never mastered anything but English. You may be taught other languages in school but if you are never immersed in them for any period of time you never feel comfortable reading, writing, or speaking a foreign language. My unscientific observation is that most Germans are fluent in both German and English. In Germany is English taught in all schools? How do people become fluent in both German and English? If you are truly bi lingual, what language do you “think” in?
English is a mandatory second language in virtually all levels of education in germany. This hasn’t always been the case, so the ability is more widespread amongst younger generations.
It is also worth noting that due to the way we learn english (primarily by reading/writing and possibly listening) those disciplines tend to be much better developed than actually speaking the language, simply because we rarely get to in everyday situations (and if we do it is almost always with another European national who has learned the language the same way we did, and struggles the same way).
On the other hand, this often leads to Europeans correcting english speakers on their grammar, because native english speakers learn the language primarily by hearing and speaking it, and there/their/they’re and such sound way too similar.