Translation of predominantly in German

So by age twelve, I had decided that I wanted to learn English and I was studying for the United States TOEFL at age twenty. Being bilingual practically from birth, makes speaking languages very easy for me.
I had never heard the phrase before. In America, there are also different idioms than here in England. It seems that the Americans say it differently than we do here in the United Kingdom.
I am glad that you accepted my offer. I would like to write letters and emails in English and if you want you can write back to me in German. I want to correct your German and so we will both get better.