If I would complain about any new language or environment I’d be dropped in, I’d probably in the loony bin by now.

Tell the team leader that you don’t know the language but are willing to learn, read the existing code which will give you a feel for the language, the project, and the local programming style, all in one go, and you should be fine. Imagine the backend was written in PL/I, Prolog, or LISP instead of just another ALGOL dialect ;-)