Include current value of language toggle as URL parameter

[daogrady]

Currently, toggling between Java and node.js does not seem to persist the user's choice in the URL parameters:

Screen.Recording.2025-08-20.at.09.08.00.mov

I can see that there is logic in place for writing and reading this URL parameter, but at least the logic for writing appears to not be executed as of today (therefore labelling as bug).

I would expect the toggle value to be included in the URL parameters, persist across subpages, and even take precedence over the value read from localStorage.

The current behaviour can lead to confusion when a CAPire guide is shared and users see different content, based on their local language setting.