national language; state language
Refers to a language officially designated by a country, often in legal or political contexts. Compare 国語 (こくご), which can mean 'national language' but also 'Japanese as a school subject'.
See also: 国語 (こくご)
In that country, the national language is stipulated in the constitution.
Multilingual nations may have multiple state languages.
公用語 means 'official language' used in government and public institutions, which may overlap with 国家語 but can also include languages not designated as the national language.
Compound of 国家 (nation, state) and 語 (language).