Language and Template in preview cache id

Language and Template in preview cache id:

- [X] test coverage
- [X] finish the code
- [ ] 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