what differences between do you speak english and do you speak in english?
Do you speak english? Commonly said. Do you know English?
Do you speak in english? Not commonly said. I'd guess it perhaps means 'Is English the language that you use? (eg Or do you prefer to speak in Swahili?)
I have one more question. What differences between borrowing costs and costs of borrowing? If you can explain me. I am not englishwoman. I don't understand.