need one for brain plasicity. it would be nice to be able to easily learn a foreign language or musical instrument naturally.

Easily? Have you ever actually learned a second language or an instrument as a child?

There is one!

Ketamin should have huge impacts on neuro/brain plasticity when used properly (i.e. in therapy)

Psilocybin has this effect. Source: I can't remember where I read it, so low confidence.