Mother tongue is the living language which one learns in one's childhood (as one's first language) and in which the person generally speaks with the members of his/her family and which one, free of all influences and true reality, declares to be his/her mother tongue. The mother tongue of the dumb and the infants unable to speak is the language in which their next of kin regularly speak.
12. Language spoken besides mother tongue
The living language besides mother tongue is the one in which the person is capable to understand and to make him/her understood by others. In case the person speaks several languages other than the mother tongue the one mostly used will be marked.