ES primera lengua / CAT primera llengua / FR langue première / DE Erstsprache

A person’s first language (also, L1) is whatever language he or she uses most frequently because it is the language over which that person has fullest mastery. It is also the language in which a person can handle most situations, in most contexts, modes of use and registers.

The adjective ‘first’ can be understood in two ways: in a chronological sense, since it is the first language one acquires (hence coinciding with the mother tongue); or in the sense of predominance in terms of mastery as explained in the previous paragraph, and then it does not necessarily coincide with the mother tongue. In the latter case, the mother tongue need not be poorer in terms of expressive resources and number of contexts of use, but it may remain in an underdeveloped phase in terms of literacy and the possibilities of diaphasic variation.

In the field of language teaching, the term ‘first language’ is usually set in opposition to ‘additional language’ (also called ‘second language’ or ‘foreign language’). ‘Second language’, in turn, is also used in two ways: either as an equivalent for ‘foreign language’, especially in the phrase ‘teaching and learning of second languages’; or as the language of the learner's social context, as in the phrase ‘Portuguese as a second language’. In that case, the adjective points to the fact that the language that is being learned is publicly used on a general basis in the learner’s social environment (e.g., learning Portuguese in Lisbon), while ‘Portuguese as a foreign language’ means that this is not the case (e.g., learning Portuguese in Athens).