The latest Definitive Edition of the game actually allows writing code using Ensemble Studios' original scripting language, XS. There are some great docs on it here: https://ugc.aoe2.rocks/general/xs/
The scripting functionalities, such as built-in functions, are still getting expanded with most major updates.
There is also a python-based tool for creating and editing scenarios and triggers via python scripts called AoE2ScenarioParser - and a lot of people are using it as well!