D10 Compatibility + Support overriding langcode ids in parameters

I've, perhaps, made this patch bigger than it needed to be. Because it has two updates:

• Updates to allow for D10 compatibility (dropping D9 and lower)
• Adds support to override the langcode value in the URL with a custom value. This mimics what is currently used for the URL prefix language negotiation which is something we need for our project.

Updating issue title and description with changes applied in MR.

Updating this to a Feature Request given the increased scope. (sorry for all the pings)

Marking as "Needs review"

This is now merged and included in the first alpha release (2.0.0-alpha1)

Automatically closed - issue fixed for 2 weeks with no activity.