In Morrowind and Skyrim Khajiti spoke in 3rd person. But why did the khajit in the game Oblivion speak in the 1st person? Even the khajiti that lived in towns in Morrowind still spoke 3rd person. (In skyrim there were no real Khajit civilians.) Can khajiti learn to speak 1st person, or was Beth trying to remove the 3rd person talking in Oblivion.

I should probably post it in the lore section, but It is game specific.

It's Khajiit. But yes, Khajiit can learn to speak in 1st person. You shouldn't look at games for 100% lore correctness, Bethesda is known to break their own lore or change it on the fly if they're lazy or don't have time to create things as they should be by their lore.

Because the voice files were shared with Argonians, who don't speak in third person. It's also why the Nords lost their accent in Oblivion, because they shared a voice with the Orcs (who in turn became a bit more chipper sounding).

I noticed it with Tsavi. It's actually dialogue specific to her that isn't shared with Argonians.

I always just assumed she was more well-spoken because she was raised in Cyrodiil or something and so she's more attuned to Cyrodiilic-style speaking instead of Ta'agra. She is part of the Leyawiin court, after all.

Actually, it seems to be true of a lot of Khajiit in Leyawiin. Even Shomara, the "dumb-as-a-post" sister of the Three Sisters Inn speaks in first person.