On this page you'll find all of Latias's Pokédex entries, along with my analysis of them.
Ruby, Omega Ruby: Latias is highly sensitive to the emotions of people. If it senses any hostility, this Pokémon ruffles the feathers all over its body and cries shrilly to intimidate the foe.
Sapphire, Alpha Sapphire: Latias is highly intelligent and capable of understanding human speech. It is covered with a glass-like down. The Pokémon enfolds its body with its down and refracts light to alter its appearance.
Emerald: They make a small herd of only several members. They rarely make contact with people or other Pokémon. They disappear if they sense enemies.
FireRed, LeafGreen: It can telepathically communicate with people. It changes its appearance using its down that refracts light.
Diamond, Pearl, Platinum, Black, White, Black 2, White 2, Y: Its body is covered in a down that can refract light in such a way that it becomes invisible.
HeartGold, SoulSilver, X: It communicates using telepathy. Its body is covered in down that refracts light to make it invisible.
Y: Its body is covered with a down that can refract light in such a way that it becomes invisible.
Well, now we know how it's so good at running away from you: it literally goes invisible.
How are you supposed to catch a Pokémon you can't see? Silph Company hasn't exactly imported the Silph Scope to Hoenn, last I checked. dubiousdisc was kind enough to remind me that the Devon Scope is a thing, which actually makes this pretty funny: this is the generation that actually has invisible Pokémon in the form of Kecleon, so why can't you use it on Latias and Latios to find them more easily?!
All joking aside, I find Latias's Pokédex entries fascinating. Here we have a Pokémon that's both intelligent and empathetic to humans, but also totally aware that hey, humans aren't necessarily a good thing to be around, and it has no qualms getting the hell away from them. Since Latias is a legendary Pokémon I can easily buy that they can communicate with people telepathically, and I actually really liked the sequence in the Gen VI remakes where you go to Southern Island and Latios/Latias seek out your help. They don't talk or anything, but it's obvious that they understand humans perfectly fine. Latias is an intelligent Pokémon and its dex entries reflect that.
One thing I do want to point out is the Emerald dex entry — while obviously there's only one Latias and Latios per game, that isn't the case in the movie they appear in — their origin story makes it clear that there are multiple pairs of Latios and Latias in the world. I wonder if that's what they had in mind when writing that entry? Of course, it could just be referring to Latias and Latias, but it seems odd to refer to a duo as "several members." It kind of seems like that while there's one instance of each legendary in the games (at least per game/generation), more actually exist out in the Pokémon world for some species like Latios and Latias. That's my interpretation, anyway.