इसलिये -> इस means this and लिये means for. So इसलिये means thats why.
Thank you, it helps to learn what the components mean.
"Therefore" is a perfectly literal translation of "isliye" and should be accepted.
Do they speak a lot of English in Delhi
Why is neccessary to write "from"?
Because of the "से." It wouldn't make a lot of sense to say "he is Delhi so he speaks English" because that makes it sound like he is the city of Delhi.
See comment above