1. mother tongue; native language
2. protolanguage; parent languageLinguistics, See also 祖語 そご
Wikipedia definition
3. First languageA first language (also native language, mother tongue, arterial language, or L1) is the language(s) a person has learned from birth or within the critical period, or that a person speaks the best and so is often the basis for sociolinguistic identity. In some countries, the terms native language or mother tongue refer to the language of one's ethnic group rather than one's first language. Sometimes, there can be more than one mother tongue, when the child's parents speak different languages.
Read “First language” on English Wikipedia
Read “母語” on Japanese Wikipedia
Read “First language” on DBpedia


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