The more the better if you can be an expert or quality level in the subjects. If you just know the basics its not worth, and i would value more an outstanding level of english than 3 european languages that are spoken just in their country.
For me the only languages worth it are: english, chinese, russian and probably spanish. The last one is a little bit biased because im from Spain.
Why in that order man:
Spanish I a lot more useful than Russian
And yes I get it but if you capable of understanding them it’s good enough. So you let people speak in the languege they are most comfortable with.
Well, first you need to get the basics of the language and get comfortable with its simpler forms. Sign up to a local course or find one online, either is great for beginners.
Then, find a person who speaks the language on a native level and communicate with him or her on a regular basis. If you can’t find a person like that, find a TV show or a series of movies on that language and watch it without subtitles. I’d take either of the two methods over just about any book out there. 
Try to find some people which speak German and try to speak with them, message them, visit them…
I would also recommend the app Duolingo to start, it is a fun and easy way to learn the basics of a new language.
I am fluent in 3 languages, here is the best language learning process imo:
English is my second language and I can tell you that even after learning for around 10 years when I moved abroad (to the UK) I still did not understand a lot. Learning the casual language and the accent is super important and you won’t get that with people who are just teaching you the language.
Make sure to learn from a native speaker I think thats your best bet. Its easier to learn this way and you can understand a lot from the context/hand gestures, also you memorise it better. Best of luck!