I haven't done international traveling with really small children, but I did a 1,500-mile roadtrip with a 3-yo and a 22-month old. I was lucky in that I got to carpool with my brother, so we were able to share driving duties-- 1,000 miles is about as far as I can handle solo-- but the drive to and from went very well for both of the kids. Having the older boy be able to entertain the younger one was very helpful, but doesn't really help with your WIP.
They were both wayyy too young for the usual car games of road trip veterans that I played when I was a kid-- license plate games, the alphabet game, stuff like that-- but I'd bought them a iPad just for this trip, and the older one got to play some games, and the younger one got to watch him, and they were as happy as clams. When I was little (1400-to-1700-mile road trips), we amused ourselves with books and listening to kids' music on a tape recorder when we got tired of watching the scenery; for this one, my brother had a Netflix subscription on his phone, so he gave the kids a few episodes of this or that when they got restless.
Peeking at some old phone videos, at 26 months, DS2 was still pretty much at the "Ehhh! Ehhh! Ehhhh!" or "Mmmmm!" stage when he had complicated stuff to discuss, although he could understand far, far, far more than he could speak on his own. Yet at the same time, he had no problem in conveying his wishes. "Ehhh! Ehh! Ehhh!" "You want the dustpan?" "Ehhh! Ehh! Ehhh!" "You want the brush?" And then he'd go sweep up some spilled Cheerios and throw them in the trash. Or, "Tell Grandma that the muffin was yummy!" "Mmmmmmmm!" But he wasn't conversational in a verbal kind of way until he was a few months away from his third birthday, when he could say things like, "I like choochoo tracks" or "My whistle" or things like that. For some of it, if you weren't tuned in to understanding two-year-old-speak, it would have been pretty hard for an outsider to interpret. So the words were there, but they weren't quite clear-- like he would say something, and it would sound like "duck" but I knew from context that it had to be "track". I had taught my kids some of the most-important-to-us baby signs-- "milk", "sleep", "play", "more", "all done", "potty"-- when they were newborns, and that really helped cut down on the frustration of not being able to communicate, and they were still using them when they were young two-year-olds.
One thing I remember from DS1-- I noticed a flier for a toddler tumbling program for 3-and-up, and he was 2-and-a-half. I thought, "Pshaw! Just six months! I wonder if he can sign up anyways--!" but of course, I didn't. And then fast-forward six months, and I was amazed at how much development he had undergone between two-and-a-half and three. So I agree that "a two-year-old" can plausibly be anywhere-- a barely-two is developmentally very different from an almost-three. In terms of cooperation and attitude, though, I found that the eighteen-to-twenty-four months involved more butting of heads and exerting-of-will than the twenty-four to thirty-six months... Perhaps mine got their terrible twos in early.
Another thing I noticed was, for example, with shirts. A baby or young toddler will let you dress him in any shirt; he doesn't care. As he grows, though, he'll say, "I want the ball shirt!" and as long as there's a ball on it, he's happy. And when he gets, say, closer to three, he'll say, "I want the baseball shirt," and by golly, if you try giving him a basketball shirt or a football shirt--- you're obviously not going to slide that past him unnoticed!
I got into the habit of giving him his choice of two shirts-- "Do you want to wear the orange shirt with a basketball, or a maroon shirt?" and he'd have that amount of control over his surroundings, and that would make him happy.
Writing kids is hard. Writing young kids is very, very hard, especially since so much of their communication is physical and relies on someone being in tune with them.
Good luck!