feat: add support for working with lang

[mhevery]

What is it?

• [ ] Feature / enhancement
• [ ] Bug
• [ ] Docs / tests

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Use cases and why

• 1. One use case
• 2. Another use case

Checklist:

• [ ] My code follows the developer guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation
• [ ] Added new tests to cover the fix / functionality

[manucorporat]

This PR introduces a new API, which implementation i am not sure it's entirely correct since use methods can only be used in rendering context, what's this for?

[DustinJSilk]

This is great, it also solves a PR I sent to get access to request headers.