Create AcceptLanguageSet that is usable in DataModel. AcceptLanguageSet is an unordered set of ordered lists. (One list would be enough to represent Accept-Language of browsers but in addition we need to support the case of multiple requested languages.) The unordered set represents the languages to keep. The ordered lists have as a first item the preferred language and the rest is the order of fall back languages if the previous language in the list has no content in the item to filter.
[ "en", "first-en-fallback", "second-en-fallback", ... ],
[ "de", "first-de-fallback", "second-de-fallback", ... ]