The higher weight language from the query-langs matchin one of the possible-langs

A query string like en-US,en;q=0.9 returns a collection of language maps:

[{:weight 100
  :base-lang "en"
  :subtag "US"}
 {:weight 0.9
  :base-lang "en"
  :subtag nil}]

Translate the key k based on dic entries and langauge l.

The default is used if not found, otherwise nil is returned.

Check if all elements have both all languages