mother language
/ˈmʌðə ˌlaŋɡwɪdʒ/noun
1= mother tongue.
2The language in which something was originally written; the language to which a word belongs or from which it originates. rare.
3A language which gives rise to others; especially one regarded as the source of a group or family of other languages.
Origin
Late Middle English; earliest use found in John Wyclif (d. 1384), theologian, philosopher, and religious reformer. From mother + language. Probably originally a genitive compound with unmarked first element. Compare post-classical Latin lingua materna, Middle French langage maternel, French langue mère.