I dreamt a dream in English

本当にすごい！When you dream in a language, that is a major step!!! 私は日本語で夢を見たいです。Peanuts and Snoopy (and Charlie Brown) are an important popular culture icons in America.

I'm especially impressed with your use of "dreamt." That's a complicated verb. (By the way, both "dreamed" and "dreamt" are considered correct conjugations of the past participle of "to dream"). とても素晴らしいです！  

* "Because" - Try not to begin a sentence with "because." It's better to include it as the beginning of a new clause in the same sentence (like: "When I woke up, I felt somehow strange, because I had never dreamed in English before.")

** I changed the sentence one way, but you could change it differently. Did you mean "I dreamt in English because during the day I was studying English" or "The things I learned in English affected my dreams"? Both could be true.

Also, you correctly knew when to use "affect" rather than "effect"!!! I think most native English speakers (including me, sometimes) get that wrong. ブラボ！！