What language do they speak, what exactly is ELDIAN?

He is telling her about his urge to die

Is it possible they're speaking another language, not Japanese, like the gooner show Mushoku Tensei, where the fictional language is simplified to Japanese, because people need to understand.
Imagine a guy who ends up in the AoT world and not being able to understand a damn thing. Has Yams ever told us about it?

I checked a Japanese raw of Ramzi and halil, the text is horizontal to indicate they are speaking another language. Ramzi's dialogue is also shown with a squiggly line before the apology scene.