Hey man, I've actually debated with that issue a bunch of times. How fluent are you in english? Can you have a conversation in english normally, or do you need a translator next to you at all times? If I were you I'd probably read a bunch of stuff in english: news, books, other MC's lyrics, whatever. But this is to help you with your rap flow. Secondly, do you already write in german, or are you starting directly in english? I'd practise in english, and what I'd do is translate your own lyrics and then adapt the english version to the beat. I'd this for a few times, until your start feeling confortable at raping directly in english (and read some books in english to expand your vocabulary). Hope this advice helps. Peace