translating menu option extension to fr and de, adding help and sanity check

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | not needed
see also https://github.com/symfony-cmf/SimpleCmsBundle/pull/124#discussion_r16293166