Hardware acceleration removal would mean no OpenGL/DirectX is being used?
Yes, only as an after-thought for speed if enabled during build.
"Usage of another language means that another language is used, so is that the reason that you cannot agree to my statement that only one language is used?"
Did you seriously skip the whole article, looking for the first link? The fact that it uses Cairo is irrelevant: it is what it does, not how.
Menus and similar "Control Graphical components" are usually implemented using other libraries, but can be implemented using one of (many?) rendering APIs like OpenGL and/or DirectX.
What if I told you that window toolkits like GTK+ don't need to and probably don't use OpenGL/Direct3D? 3D hardware rendering is unnecessary.