In his Tucson, Ariz., backyard, 10-year-old Linken Kay throws a ball for his dog, Harley.
The dog speaks only English. But Linken was raised speaking another language.
"Li ŝatas salti en la naĝejo por preni la pilkon," Linken says.
What's that, now?
"I said, um, he was going to jump in to get the ball," Linken explains. "And he likes to jump in and get the ball."
Linken is a rarity: He's a native speaker of Esperanto.
More than hundred years ago, a Polish physician and inventor had an ambitious idea: Create a language that anyone could learn easily. The hope was to promote world peace through a universal tongue.
It took several decades, but eventually L.L. Zamenhof designed Esperanto.
Although the language hasn't become as popular as Zamenhof hoped — or brought world peace — it's estimated that anywhere between 200,000 and 2 million people speak the language worldwide. Devotees say Esperantists exist all over the globe, with especially large pockets in Europe, as well as China, Japan and Brazil.
The popular language-learning platform Duolingo is even about to issue an Esperanto app.
But there are only about 1,000 native speakers, like Linken. Esperanto was his first language — and still the main one he uses with his dad, Greg Kay.
Greg fell for Esperanto when he was his late 20s and going to school in Japan.
"Having lived abroad, I realize that the language barrier is a significant barrier, and can create many misunderstandings," Greg explains.
He used Esperanto while traveling when he was younger, bicycling between Esperanto-speaking homes in Korea. He used a free hospitality network, called Pasporta Servo, which lists Esperanto speakers willing to open their homes to fellow Esperantists. Pasporta Servo still exists today.
"Thanks to Esperanto, I've met many people that I would have just passed by otherwise — many fascinating people," Greg says.
Esperanto creates a kind of "level playing field," because it's a second language for almost everyone who speaks it, says Humphrey Tonkin, an English professor at the University of Hartford in Connecticut. He taught himself Esperanto at age 14, and then used it to travel across Eastern Europe and beyond.
"The result is that you're kind of lifted out of your own cultural limitations," Tonkin says. "And you're really in an authentically international environment."
That was the hope of Esperanto's founder, Zamenhof. He wanted to bridge differences between people, especially religious differences, Tonkin says. Zamenhof was Jewish, and many of Esperanto's earliest adopters were also Jewish. They connected with this new language that emphasized equality, Tonkin says.
So many years later, the language has grown far beyond Europe's Jewish community, but hasn't taken off as Zamenhof envisioned. When Zamenhof died in 1917, Tonkin says he was "deeply disillusioned."
It's hard to know what it is about Esperanto that has kept it from blossoming, but Tonkin calls it a language of "low prestige," one that's still a bit hard to explain to those who've never learned it.
"When I say that I speak Esperanto, they say, 'What do you do that for?' since I appear to be a perfectly normal person in every other respect," he says. "Or they say, 'I heard about that once. That died, didn't it?' "
Not only has it not died, but Tonkin thinks it might actually be growing, though he says it's hard to gauge an accurate number of speakers.
Even if Esperanto's reach is static, the language has survived against some steep odds. The rise of English could have easily killed it off, Tonkin says. Or it could have faded away during both world wars, when its speakers were persecuted. But Esperanto kept going, and Tokin thinks idealism probably had a good part in it.
At this point, learning it is kind of, "dare I use the word — a utopian thing?" Tonkin says — especially since the world is full of problems.
"That's all the more reason for hanging on to those things that will make the world a better place," he says. "We just need to get together better, and maybe Esperanto is one of the ways we can do it."