what programming language would be the closest to mIRC?

It depends, a lot of C/C++ syntax is similar to mIRC's, but I found a lot of the functions are very similar to vb's.

It depends if you want similar syntax or similar functions, also, even if you find a language very similar to mIRC scripting.. the language will most likely still be a lot harder.

if you mean: ( from Khaled's FAQ )

Question: In which language is mIRC written?

Answer: mIRC is written in a mixture of C/C++, in pure win32 code, and compiled under Visual Studio .Net Pro. mIRC was originally developed under Borland C++ v5.02 however.
I used Borland C/C++ v5.02 because it allowed parallel development of 16/32bit code from the same code-base. This isn't important anymore because the 16bit mIRC is no longer being developed.