In the Kenyan context mother tongue is regarded as the language of the school catchment area. First language is regarded as the language acquired before none. Some vernaculars are mother tongues and first languages.
First language and mother tongue have basically the same meaning, whereas the vernacular is the language spoken by the people. There was a time when Latin was the language well-to-do people used as a means of communication, no matter what their mother tongue was. At the same time, the majority of the people were using their mother tongue like: French, Italian, German.
Your mother tongue is your first language. However, it may take the form of any of the varieties spoken in your region. Among these, only one variety is the standard while the others are non-standard , vernacular languages.
Up to my knowledge in TEFL and the related acronyms such as "L.1, L.2,MT, NL and the alike"I can simply illustrate the difference in the forthcoming lines:
"mother tongue" MT or "native language" " NL": has the following meanings:
1-It is associated with one's culture, religion and ancestors. “Mother” conveys the meaning of homage to “motherland”, the place(s) where one's descendants lived and originated.
2- mother tongue is the language “spoken at home to our parents” or or the language “our parents taught us” In this sense it has the power of rapport and intimacy" Physical and spiritual Closeness
As for the first language, it has the following meanings:
It is the dominant language as the language(s) we’re fluent in.
The language we speak every day and don’t hesitate speaking. For me, it’s English – in India.
It is more like lingua franka
Thus it is wrongly to associate the English language with the phrase “mother tongue”. English is taken for granted as a universal language.
When we speak about mother tongue, we tend to think of a common language spoken by a cultural group or our ancestors. First language and dominant language as the language we’re fluent in, the language we speak every day and don’t hesitate speaking. A vernacular language is the native language of a specific population, especially as distinguished from a literary, national or standard language inhabited by that population.
As a baby, I learned 2 languages simultaneously, so both are my native languages. The Mother Tongue is the idealized languages you know. The vernacular is the way that most people in a culture speak, including grammar considered wrong by those who believe in an idealized, generally older form of the language.The vernacular includes slang and new words in the lexicon.