This. I used to go to Germany with British mates and we spoke German to each other - even when there were no Germans around - you have to completely immerse yourself in the language. So, go to Spain with Spanish people, or Spanish-speaking Brits, and forget English for a bit.
I was once in a hotel with a Dutch family on the next table: the kids were about 6 and 4, the father (who was speaking nothing but English) was asking the kids what everything was in English by pointing at it (a fork .... a knife ... a napkin etc). If the kids answered in Dutch, he'd keep on...
There are two types of people who learn German: those who have done Latin at school and those who haven't. If you're the former, you'll find German grammar pretty straightforward; if you're the latter, German is going to be tough.
As I said, I went from beginner to fluent in about five years...
I've dabbled with Duolingo and didn't find it that useful TBH.
I'm with Herr T, the only way to learn is to immerse yourself in it with a live partner and speak nothing but that language. I find evening classes are useful particularly if you go at a higher level than you actually are.
When I...