Arkadiusz writes (and I translate):
I’ve started learning English with the Antimoon Method. After a very short time (just two months), I can already see considerable progress, which motivates me to keep working. I have a question about input. I use various sources: some of them American (mostly cartoons and TV series), some of them British (podcasts, radio). Can mixing two different kinds of English be harmful? Should I concentrate on just one dialect of English?
The only risk I can see is that you could pick up a “mid Atlantic” accent (a mixture of British and American pronunciation). This shouldn’t be a problem in any serious sense of the word, but if you’re interested in having a pure RP or GenAm accent, you should learn about the differences between British and American pronunciation (individual sounds and word pronunciations) and pay attention to those differences as you listen to content. This should help your brain keep the two pronunciation models separate.