Maintain requested language - handling content areas

Description

1. Given a specific piece of content (the page) is requested through the REST API with a specific requested language
2. Language of the response (content language) is resolved based on requested language, available translations as well as fallback and replacement rules for the page.
3. All expanded properties should try to match the content language, to return a single consistent translation.
4. All links should try to match the requested language