She likes being complimented by her human and trills about this.
"I like listening to humans so I've tried really hard to learn words! But making them means I have to run the recognition process in reverse."
"It really varies? I can understand other eevees really well, but the less a pokemon is like me the harder they are to understand. With another eevee - " Pause to think, then: "There's two ways of talking? But they're not both 'talking,' your language just doesn't have enough words. But the way everyone uses all the time is the immediate way. It's body language and sounds, and I think there's a bit of kinda psychic stuff, because espeons are really good at reading people and really easy to understand, but umbreons come off kind of... Flat."
"You can communicate about emotions with that, and stuff immediately around you, and actions in the immediate past or future - like a command for someone to do something now, but there isn't a default thing that means a time so you can't say specifically when. You can also communicate... Simple? Emotional? Opinions and intentions about something someone else brought up."
"But then there's also the... Depth way? If you want to talk about distant stuff, or really abstract stuff, or complicated opinions with a lot of caveats and if-then. And that's psychic. It's harder if you don't know someone or trust them, and it's harder with non-eevees and harder with pokemon less like us. It's easier with psychic types, and impossible with dark types. So espeons facilitate discussions a lot, but umbreons can't really depth talk to anyone else."
"You can also kinda guess which eevees will be espeons or umbreons based on how reserved or communicative they are."
"And words are less communicative than the depth way, but more communicative but not as quick and easy as the immediate way."
"Umbreons might actually have a words language, come to think of it, but I don't know it."