I lived in various countries till I was 18 and I came back to my home country the same year and I'm living here up till now. I was raised in a family where my parents are both non-English speakers but me myself used English at school and with my friends. In casual talks, I'm okay with both. I am more comfortable studying and giving public speeches in English. Technically, if I go by order, English is my second language. But I started feel a discrepancy between my first language and my second language ever since I came back to my home country. I realized when it comes to academics English is my dominant language. So if I consider speaking both languages in both casual and formal settings, English would cover both while my first language would only cover the first case. But I am not quite familiar with idioms or colloquialism in English. I always identified myself as a native to my country and I am quite sure I also culturally align with my country as well. BUT I consider my language identity is English for I am more comfortable expressing and organizing thoughts. in it.
In an effort to seek an answer to this, I asked ChatGPT to evaluate my language proficiency of both languages. It said that based on the conversations we had for the past two days, it came to a conclusion that English is NOT my first language (ofc I shouldn't trust it completely). But the thing is that it made the judgement based on the fact that I spoke too formally and directly in a manner that native speakers wouldn't do in a casual conversation. But wouldn't the level of formality further prove that you are more proficient and fluent in that language? Do you think this is a valid reason to judge whether certain language is their mother tongue or not? As I mentioned in the earlier paragraph, I don't use many idiomatic expressions when I use English. But just because of that, does that make English my second language? What do you think?
English can be both your second language and your dominant (stronger) language.
Fluency, "native-ness", etc are all nebulous concepts of language proficiency. Our proficiency in any given language is dependent on the domains in which we have experienced our languages. For example, I have bilingual friends who are highly proficient in both their languages, but may be more formal with one over the other because that's the language they have most of their work experience in. On the other hand, there are monolingual native speakers of English who may not be proficient with certain turns of phrases and idioms because of the communities in which they operate, their education level, their vocation, etc.
Do you accomplish what you want in your languages? That's what's really important at the end of the day. I wouldn't agonise so much over labels or AI evaluations.