National language

A national language is a language (or language variant, e.g. dialect) that has some connection—de facto or de jure—with a people and the territory they occupy. There is little consistency in the use of this term. One or more languages spoken as first languages in the territory of a country may be referred to informally or designated in legislation as national languages of the country. National and/or official languages are mentioned in over 150 world constitutions.

C.M.B. Brann, with particular reference to Africa, suggests that there are "four quite distinctive meanings" for national language in a polity:

The last is usually given the title of official language.

Standard languages, such as Standard German, Standard French, and Standard Spanish, may serve as national (language-in-common), regional, and international languages.

"National language" and "official language" are best understood as two concepts or legal categories with ranges of meaning that may coincide, or may be intentionally separate. Stateless nations are not in the position to legislate an official language, but their languages may be sufficiently distinct and well-preserved to be national languages. Some languages may be recognized popularly as "national languages," while others may enjoy official recognition in use and/or promotion.

In many African countries, some or all indigenous African languages are officially used, promoted, or expressly allowed to be promoted (usually taught in schools and written in important publications) as semi-official languages whether by long-term legislation or short-term, case-by-case executive (government) measures. To be official, spoken and written languages may enjoy government or federalised use, major tax-funded promotion or at least full tolerance as to their teaching and employers' recognition in public education, standing on equal footing with the official language(s). Further, they may enjoy recognition as a language used in compulsory schooling and treasury money may be spent to teach or encourage adults in learning a language which is a minority language in a particular area to restore its understanding and spread its moral stories, rhymes, poems, phrases, songs, and other literary heritage which will promote social cohesion (where other languages remain) or will promote nationalist differentiation where another, non-indigenous language is deprecated.

...
Wikipedia