Set headless browser language from fetch configuration

[Ndpnt]

Currently, only the HTTP Accept-Language header uses the language defined in the fetcher configuration.
However, the headless browser itself is not updated to reflect this setting.

This can lead to cases where the requested page does not fully respect the configured language, since some sites rely on the browser’s reported language rather than just the request headers.

• Detected in add skoda id france-declarations#608
• The document at https://skodaid.vwgroup.io/data-privacy respects the language when the browser’s language is properly set.

The solution is to extend the fetch configuration to also update the headless browser’s language settings (navigator.language, navigator.languages).