As someone who started studying English at the age of 8, with 2/3 languages already in the mix, I immediately perceived it as my language because I had a more consistent relationship with it and could take it with me in other contexts no matter where I was.
My family moved a lot, therefore I grew up in a variety of contexts and finding one identity to conform to was not an easy task. I went to an international school in Malaysia and that is where my journey with English began. I later moved to the U.S. for just under a year, but to this day it seems as though those were the experiences that led to me knowing English and becoming an English teacher today. That could not be farther from the truth, and I realised that well into my adulthood.
Before my big realisation, I continued to validate my knowledge and skills as an English teacher saying things like “I’m from Armenia, BUT I teach English because I used to live in Malaysia”, “BUT I attended a school in the States”, “BUT I speak English daily to my brother-in-law who is Irish”, or “BUT my grandma used to be an English teacher”, and the list goes on.
It wasn’t until I went to a conference that I spotted my own flawed narrative which gave little to no power to the main character of my life: me!
Why was I not giving myself credit for learning and studying to become an English teacher? Why did I have to distance myself from my own origin to comply with some kind of “norm” that in order to know English, you had to have come in touch with an anglophone culture, or you must have had a distant relative who spoke English to you as a child! It was paradoxical that I was trying to justify having this skill in the way that I was, and it took me several attempts at presenting myself at conferences to catch my own bias towards myself.
Flashforward to the present day:
I am totally confident about being who I am as an English teacher.
I smile when someone asks me if I’m from England or from the States. I say I am neither, I am Armenian.
I no longer feel there is a need to add anything else other than “I’m an English teacher” to anyone I meet for the first time…
…this is obviously followed by the question “where are you from?” with the anticipation of placing me in an anglophone context, and to which I answer, “I’m from Armenia, English is not the official language there, or the second language people speak”.
Most of the times, my confidence in saying that conveys the right message to my interlocutor and they begin to connect the dots. I feel that since my mindset has shifted, I can do much more for the non-native speaker category and help others make the same realisation, that is to say: a skill is not intimately tied to one’s birthplace or experience growing up in an English speaking country.
I’ve created this little worksheet for you that you can use to keep your impostor syndrome on track. Please use it and share any interesting finding in the comments.
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The Non Native Speaker 
I agree with what you’re saying here. As you said, native speakers are unaware of the use they make of…