What is mother tongue?

What is my mother tongues? Recently I read the news about Hong Kong people's mother tongue. What is my mother tongue? First language? Second language? What does it mean mother tongue/1st language? Many Hong Kong Chinese moved away from the ancestral land. Mine is Teow Chew/Chao Zhou.

I don't speak Teow Chew, a branch of Minnan language group. I can understand some daily Teow Chew because of my parents used Teow Chew, when I was very young. I went to school and most of my peers are Cantonese speaking. Thus, I guessed my first language was Teow chew. I started learning Teow Chew recently. My Cantonese is definitely more fluent than my Teow Chew. I was using English textbooks in most of my education. Thus I consider I am more fluent in English for my work and study.

Ethnolinguistics is a branch of study about the relationship between an ethnic group and the languages(written and spoken). In the Chinese language/dialects context, spoken language can be quite different from the written. The writing styles of Cantonese speakers can be very different from other Chinese even though we are using the same writing scripts either in traditional characters or simplified characters. This is a slide in my presentation about "Engaging Chinese Diaspora for Bible Translation Ministry. One of my unresolved questions is "What does 'Chinese-ness' mean?" Who can and Who should define the term? Where is our ancestral land, I believe that all people were coming from the same boat. We are the diaspora of some kind, diversity with unity. What are the implications of this? How do you think?