(adj) able to speak a language very well and easily
fluent
(noun) the language that is used most for communication in a country
official language
(noun) a form of a language that is spoken in part of a country
dialect
(noun) the first language you learned to speak as a child
mother tongue
(adj) able to speak many languages well
multilingual
(noun) a person who speaks a language as their first language and hasn't learned it as a foreign language
native speaker
(adj) able to speak two languages perfectly
bilingual
noun) a way of pronouncing a language that is connected with the place you come from
accent