I read, write, think and dream in both, German (my mother tongue) and English (the second language). I bring it down to one fundamental difference: English is an easy language to pick up. Grammar is simple and vocabulary is pretty straight forward, at least for anyone from the Roman/ Indo-Germanic region. German is overwhelmingly ruled and structured and grammar is quite complex.
At the beginning.
As you progress with your language skills this changes. English becomes increasingly more context driven where choice if word makes all the difference. There is a different word for every situation and usually more than one. The quality of speaking becomes more and more vocabulary driven.
German is hard to begin with. There are three genders, male, female, neutral and there is absolutely no rule to what has which gender. Strangely it seems like when a new word is adapted Germans attach a gender to it like “der Computer” and everybody agrees, somehow. But German has this wonderful way of words: you can make them up. You can put words together to make new words from your basic vocabulary (yes, there are rules to it too). It’s also how German has those famously long words, but really they’re just compositions .That way German actually becomes easier as you progress.