official language
Refers to a language designated by law or regulation for official use in a country, region, or organization.
スイスでは四つの公用語が認められている。
Switzerland recognizes four official languages.
公用語 is a language officially designated by a government or organization for administrative use, whereas 共通語 simply refers to whatever language is commonly understood, official or not.
公用語 is the language(s) officially designated for government and public use, whereas 標準語 refers to the codified standard form of a language itself, regardless of its legal status.
official languages of the UN
Compound of 公用 (official use) + 語 (language).