Presumably joking. She just enjoys being silly, even if her only audience is herself.

It doesn’t work automatically, you have to spin it manually

I would actually argue it’s somewhat the opposite: creatures such as the fae, that can move between worlds, have been visiting both and bring a tidbit or two back and forth on occasion, and thus the commonalities we see between the two worlds was mostly brought to Earth first.

We know there is a time differential between Earth and Innworld (time passes quite a bit faster on Earth), and many of the things that are similar haven’t been around nearly long enough on Earth. English, for example, is only about 1600 or so years old, and the oldest parts of the language don’t resemble modern English all that much. Given the time difference, there is no way that Innworld Common became the sole language of the entire planet in only around 400-500 years or so, with seemingly no records of any older spoken languages.

But, if world hopping creatures instead brought Innworld Common to Earth, it could have gotten corrupted by the existing languages here, which is how we ended up with things like Old English. As those creatures continue to visit Earth over the centuries, they keep bringing the language closer and closer to Innworld Common, until both it and modern English are fairly close. At the same time, they bring back tidbits from other languages from Earth, which is why we see a few examples of things like Latin, or French, etc.

“Don’t worry, Swifttail. I’m hardly about to start a huge incident. Underhanded pettiness requires a reply in kind. Thus, I’m sending Erin Solstice after them, of course. Or haven’t you heard that the Assembly of Crafts is already having to explain a tax on Liscor’s magic doorway?”

Olesm hadn’t. But he gulped anyways. Pallass might be a Walled City, but he imagined Erin was a match for it. Ilvriss grinned predatorily.

Erin: the last resort and ultimate weapon.

“No. She doesn’t appreciate rank.”

“Ah, you’re visiting her.”

The other two Drakes sighed. Osthia looked confused. Ilvriss made a face that was partly over exaggerated, but he nodded.

“Captain Blackwing, I’ll be back. I need to visit the first of what might be unusual allies. At the very least, she’s thwarted Az’kerash again. Which means that Erin Solstice has the support of Salazsar.”

“The [Innkeeper]? But what can she do?”

Ilvriss turned, his claw on the door. He twisted the ring and the spell went out. He smiled, for once with genuine humor.

“I don’t know. But I imagine that’s why she’s an asset. No one knows what she’ll do next.”

The way other characters talk about Erin like some kind of entity or force of nature is great.

Uh oh wall lord guy is gonna die soon, that’s a fat death flag there, we’ve seen it all too many times, I can already feel it in my bones… he’s gonna die…

Best shot?
Probably Olesm right? But he really fucked up recently…
Other than him…
There is no one really, I think. Ilvriss, Halrac… maybe. But they are quite a bit older than her I think. So it is less likely.
One of the Doctor sidestory characters potentially, when they show up in the main story.

It’s Ilvriss Gemscale, actually.

Perhaps in our world he’d be something like: Ilvriss Gemscale, Duke Salazsar