@neauoire Depends on what you will be writing in your language of choice and what your deadlines are. I'm very glad I know Python because of its massive collection of high quality modules. There is no way I'm reimplementing all of that in a bespoke language.

Also, good languages let you write good embedded domain specific languages, so making your own from scratch becomes unnecessary. Lisp is a famous example, but (G)ADTs in Haskell are IMHO even better.