[ResourceBundle] The date type has been improved

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

You should call on both strings `strtolower()` or `strtoupper()` as you call case-insensitive call line below.