But if I wouldn't speak english, I had to read german news only or couldn't use stackoverflow. 90% of the newest technology would be useless for me, because I couldn't read any documentations or tutorials.
While my spoken english isn't very good I'm able to read advanced technical books, manuals, news, and other texts without any problems.
I rarely have the opportunity to speak english. That's the problem.
From my (potentially quite flawed) understanding, English, French, and German are all good languages for capturing technical concepts, but English won out in general, simply because it's much bigger - more native speakers (thanks USA) and more widely spread (thanks British colonialism).
"... German advanced to become one of the most important languages of science and scholarship, and at the beginning of the twentieth century ranked above English and French, especially in the sciences. In order to keep abreast of the latest developments, scientists and scholars all over the world learned German, a circumstance that contributed to German’s becoming one of the most widespread foreign languages. With the end of the First World War, the “primal catastrophe” of the twentieth century, a reverse tendency arose. Germany and Austria had been economically ruined by the war and were in no position to invest in research and knowledge to the same degree as before. ..." (from http://www.goethe.de/ges/spa/pan/spw/en3889454.htm )
I'd suppose the closest thing to a nazi-controlled-germanized-europe would be the USSR (people escaping, restrictions on freedoms hindering creativity, no colonies speaking the same language, trade issues with the rest of the world) which in fifty years failed to establish a linguistic dominance even in aligned countries.
#1 read english books. translate every unknown word from dictionary. the words improve vocabulary; the sentences improves grammar.
#2 watch english movies with english subtitles. this helps greatly in understanding the accent. plus english in movies is a hell lot easier than the one in books.
#3 talk to yourself in english. there was a period in my life where all my thoughts were in english. it makes you comfortable with the new language.
ps: these are just general points - your english is pretty good!
Understanding what you are hearing, recognizing words is a very specific skill and to get better at this we need to practice this specific skill, we need to get over that annoying stage when you just don't understand what they are saying and you need to listen to it five times to finally get it - when you turn on subtitles you may practice other skills (grammar, vocabulary... skills which can be better acquired by reading books) but you basically turn off acquiring 'understanding' skill. That's one of the reasons why there are so many people who are very good at grammar and vocabulary and can easily read and write but cannot watch a movie or talk to someone because they cannot understand spoken word.
They're not wrong. It's just that you're right.
If they're bothered by the imperialism, then they should get to work translating.
When someone in US says good communication skills are important, they think it's racist.
I am from Pakistan. When I tell colleagues to master English, they think I am still mentally under British imperialism.
There is a huge trove of knowledge on the internet which you can only benefit from if you can read/write English.
It was only after I focused on my English that I was able to stay up to date with latest tech, prevent reinventing the wheels and get remote jobs. I could always feel that English gave me a superior advantage over my colleagues.