Answer 1

The Elementary SDK makes use of Vala, and nothing on other languages is mentioned on its page. In any case, you can use GTK+ and make an application that follows its recommendations on the construction of graphic interfaces.

I've seen people using Granite to extend GTK and program applications for Elementary with Python, but there seem to be some limitations:

- https://elementary.io/docs/human-interface-guidelines#what-design-is-not

- https://elementary.io/docs/code/getting-started#developer-sdk

- https://gist.github.com/mariocesar/11290827