Getting my German to the same level I understand and speak English (or Dutch) is such a massive project that I've never really bothered making time for it. I always have more interesting things to do. And if I don't there's work. Learning a language is a big time commitment and the in between state where I can't really use it without sounding like an idiot just isn't that useful to me.
I've also forgotten most of the French I knew even though I was getting quite good at it by the time I dropped the subject 30 years ago. I chose science heavy classes instead of language heavy classes (the Dutch system makes you choose). So German, Latin, and French were out. The endless & mind-numbing memorizing of words, grammar, etc. was a big contributor to that choice. And I also enjoyed other classes a lot more generally. However, I had English until the end (six years) and was actively reading English books, watching BBC, etc. by the time I entered university. In university some of my books were in English. A lot of online content was English. Immersing yourself like that is what needed to master a language.
English has kind of taken the place of Latin. It's the world's most popular second language. Without it you are a bit marginalized to specific areas or groups of people.
But we might not need it much longer if translation tools keep on improving. The key moment will be if you can have an intelligent conversation with somebody without having a single language in common. Even if it is just in written form, it would matter a lot.
I've neglected my German and French since school, but found that I could still get to a basic level of conversation later in life by just trying when I was on holiday in those countries while still living in the Netherlands. YMMV.
I do well in German and Swiss German, so I can sometimes parse other Germaninc influenced languages, but it is a matter of luck which words are used.