A language-range matches a language-tag if
it exactly equals the tag, or if it exactly equals a prefix of the
tag such that the first tag character following the prefix is "-".
The special range "*", if present in the Accept-Language field,
matches every tag not matched by any other range present in the
Accept-Language field.
The prefix case is not handled by Representer#pick_best and/or BasicRepresenter#preference_for_language
RFC 2616, section 14.4, states:
The prefix case is not handled by Representer#pick_best and/or BasicRepresenter#preference_for_language