There a lot of microcontrollers to create a robot. Examples: PIC, Atmega, 8051, STM32, ESP 32.
Currently Arduino board is very popular. because there are many libraries and so cheap.
IDE arduino You need to know C / C++.
Mplab X IDE for microcontrollers PIC you will code using C language.
STM32 are 32 bits microcontrollers. It's so good and you can configure pins using Graphical Interface (STM Cube MX). I used Keil IDE with C language.
Raspberry is a computer So it's expensive but you can coding using high level languages like Python.
If you new in embedded system then I recommend Arduino with C/C++.
All microcontrollers can coding using Assembly but It's so so hard. To learn Assembly for microcontrollers I think 8051 is great and simple.
Well. Depends on the platform you are using for your project.
Arduino? The official IDE uses c/c++
Raspbian - mostly used python but you can use any language that supports IO pins.
Windows IOT core - mainly c#
PIC? There are several compilers for C, basic etc.
As long as there's a compiler for your platform you can use any language.