What languages are used for programming inventions and devices?

Any one can apply.
The most common embedded OSes used versions of Linux, except where the native c/c++ and has Python and Java you can put js and bash everything.

Rarely used something esoteric - the more expensive the device, the easier it is to push the normal percent of normal OS and not to bathe with restrictions.

You can start with JS
so MK - amperka.ru/product/espruino-pico
or a constructor - amperka.ru/product/yodo

Usually uses C, C++, Python and js. Very rarely Lisp and Java.
But it would be better to use Rust, Julia, Purescript, and Scala.