Would a person forget how to speak their native language if they hadn't spoken it since their early teens?

My bet is that language acquired in childhood would be difficult to erase, particularly if everyday fluency were extended into the teen years.

It might depend how good the person memory is in general.

https://en.m.wikipedia.org/wiki/Cynthia_Ann_Parker

Cynthia Parker was taken by Comanches when she was 10.
25 years later she was brought back to white civilization and had difficulty speaking English.
The book to read is Empire of the Summer Moon
https://www.google.com/search?q=empire+of+the+summer+moon&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari

I imagine that would depend in part on how long ago “early teens” was. It could be five years or fifty, and that would make a difference.

What I’ve heard from people in this situation is that they may remember their original language well, more as a hearer than as a speaker, but that when they visit “back home” they are found to have a strong American accent.

I don’t actually see what “a rather obscure country with a distinct native language or dialect” has to do with it. Whether it’s Spanish or Seediq, wouldn’t we expect the individual person’s experience to be about the same?

Twenty years is the period of time, according to the detail.

My late father had moved away from his French language family at the age of 25 yrs old and moved to a predominantly English Community of which at that time ( 1940’s) he was ridiculed for speaking French.
In 1964 he went back to visit his Father who spoke French ( and little English) to my late father and he had problems understanding his Father and had to have his young Nephew translate for us. I suspect that the language used in the 1960’s changed up to modern French terms of which he had no reference to?

Yes, this does happen. They might remember bits, but their fluency could definitely disintegrate. My father worked with a woman who barely spoke her first language, and she had come to America at 15 I think. I don’t remember her circumstance or the language.

My FIL spoke Hebrew fluently, it was his first and primary language as a young child, and throughout his childhood at home. Arabic was used in the home as well. He was born and raised in Mexico, so he was fluent in Spanish also once he started school. I’m pretty sure his Arabic is extremely broken now. I’ve seen him speak Hebrew, but it seems to me he struggles. He hasn’t used Hebrew with any regularity in 50 years, except for reciting prayers, and on rare occasion when he talks to someone who speaks Hebrew and not Spanish. He stopped interacting with his family when he was 30. Mind you, with his siblings they usually used Spanish, but his parents never leaned Spanish well. His mother died when he was 13.

Interestingly, dementia patients who have changed primary language often revert back to full fluency in their original language as the dementia increases, and forget the newer learned language.

A woman in her 90s who left Japan in the late 1930s to come to the United States reverted back to her pre-war Japanese, and was completely unable to communicate in English, even with her children and husband.

@zenvelo A friend of ours had a stroke and his first language was Italian, and the language of the country he lived and worked in from the age of 20 to 70 was Spanish. The stroke affected his ability to say what he was thinking. So, the problem was not enunciating, but a disconnect to find the right words. The speech therapist recommended using his first language, Italian, and his family only speaking in Italian with him. They were living in America at the time, in Florida, so it was kind of too bad the Spanish didn’t work better for him since he was surrounded by Spanish speakers outside of his family.

It’s off topic though, because the person I knew used both Italian and Spanish up until his stroke.

We are very good at learning languages when we are young. My guess is that one’s native language stays with you.

When I was in sixth grade, we were given language instruction in French for a few weeks. I remember just about all the limited vocabulary we were given. I also remember a good portion of the Spanish I was taught in high school.

On the other hand, I took two years of German in college and remember very little of it. In preparation for a trip to Italy, I spend a few months teaching myself enough Italian to ask basic questions. I don’t remember any of it.