How do you start a development project with limited knowledge of the domain and programming language?

I am being offered to be a technical lead on a new upcoming project in my company. I have limited knowledge related to this project's domain as well as limited training in the programming language (c#) that this will be written in. I am currently a software developer and leading this project will open many doors for me in terms of experience as a tech lead, learning a new programming language and build my own confidence.

I know for sure that once I give my 100% I will be successful, but this is more philosophical.

Has anyone of you been in such a situation where you have been given an opportunity but not sure if you will succeed? If yes, how did you go about preparing yourself for such a challenge?

How do you start learning about a new domain and programming language (I am a C++ developer right now)?

Thanks MG