Learning to speak the tongue of your home country as a baby is hard enough, despite everyone you come into contact with also speaking the same language.
But, to learn English simultaneously alongside a made-up dialogue you created with your identical twin - that seems impossible.
Matthew and Michael Youlden are the only two people on the planet who speak Umeri (Instagram/superpolyglotbros)
Although try telling that to identical twins Matthew and Michael Youlden, of Manchester, England, who speak both English and 'Umeri' - a language that only two people in the world speak, and one that is likely to die with them.
You could say creating their own language has made the Youlden brothers experts in the field - and having conquered 26 languages each, I think they'd probably agree with that.
Among the languages they speak is Mandarin, French, Italian, Dutch, Spanish and even Basque - a language only used in the Basque Country - a region in northern Spain and south-west France.
The polyglot twins, who go as Superpolygotbros on Instagram, created Umeri as children - at first just started speaking it before developing the written language too.
The Youlden twins created the language as toddlers - something up to 50 percent of twins do (Instagram/superpolyglotbros)
But a common misconception of their language is that they created it so they could speak privately to each other about things - something the brothers told the BBC that it was far from the truth.
"Umeri isn't ever reduced to a language used to keep things private," they explained over an email.
"It definitely has a very sentimental value to us, as it reflects the deep bond we share as identical twins."
Surprisingly, it is understood that up to 50 percent of twins actually develop their own way of communicating with each other, although most tend to drop it over time.
"Twins have this shared language, that at some point they stop using, as if they feel ashamed of it," Matthew said.
"This is also not something unique to twin languages."
Matthew and Michael Youlden studying in a bid to learn a 27th language together (Instagram/superpolyglotbros)
He explained that people who speak a language not spoken in the area where they are living, they tend to not speak it in public, 'especially if you are raised with a minority language where you are maybe ostracised or looked at funnily at school'.
The pair never had that sort of reaction, he recalled, although adding that if they began speaking Umeri in front of extended family they'd complain: "They're off doing the language thing again."
Director of the Twin Studies Center at California State University, Nancy Segal, refers to the phenomenon as 'private speech' in her book Twin Mythconceptions,
Writing per the BBC, Segal wrote: "Based on available studies, it is safe to say that about 40% of twin toddlers engage in some form of 'twin-speak'.
"But that figure does not convey just how complex twins' language development turns out to be."
English (US) ·