

Concepts are already here - (as of now) they fix a subset of this, and errors messages can still be extremely long.
They’re less like “here’s every single template parameter of the involved types” and more like “this template thingy has many specializations with different constraints, here’s a list of all of them and why none of them are satisfied with your parameters”
freedesktop.org defines environment variables that should be used by applications to store their stuff;
[archlinux.org] has a (non-authoritative) summary, but it also provides a [link to the actual specification].