I can't think of any idiomatic expression that equals the Chinese phrase in succinctness, but a possible response with some ideas follows. You can mix and match. :) "Wow! I'm overwhelmed by your generosity. You are too kind. I'm highly (or deeply) obliged to you. I don't know what to say. Thank you so much, I really appreciate it."

I got quiet shocked,thank you very much.

overwhelmed

您好！因为工作关系从现在起不得不学习英语了，请问您可以教嘛？

Just wanna give it a try, myself not an expert in Chinese though!! ^^ "受寵若驚" --- literal translation of it is "overwhelmed by favor from superior (humble expr.)".... The nearest English expression to set the right mood is "obligation"....or, even better..... "to feel highly obliged". In English it is a show of humble gratitude to a person for his/her kind favor. Example: I feel highly obliged to you for your kind assistance. sometimes, depending on certain situations, we can replace "feel" with "am" in the above sentence.