Language and Template in preview cache id

Language and Template in preview cache id:

- [x] test coverage
- [x] finish the code
- [x] gather feedback for my changes
- [x] submit changes to the documentation


| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | yes
| Tests pass?   | yes
| Fixed tickets | #121 , #91
| Doc           | none

Merge this after PR #120