What race are the humans in Attack on Titan? What language do they speak?
The Germanic names (Jaeger, Armin, and so on) lead me to believe that the remaining humans, that we've seen so far, are descendants of Germans or at least close enough to them to receive a great Germanic influence.
As for Mikasa, her mother was the next-to-last of their Oriental clan, and her father was of a more Western heritage (having the German name Ackerman). The name &quot;Mikasa&quot; has origins in both Malagasy (of Madagascar) and Japanese (the Mikasa battleship, Mount Mikasa, or the Mikasa-no-miya[nt. 1][ref]). Given that she is simply said to be &quot;Oriental&quot;[nt. 2], we can assume the latter, and she is actually Japanese.
As for the language, it's not uncommon for countries and people who would speak little or no Japanese to be native Japanese speakers in fiction (same with English for Western movies and shows). This is generally labelled (in trope-ville) as Aliens Speaking English (which can also be true for human foreigners) or Common Tongue, essentially saying, &quot;It's easier for the target audience to understand it if everyone is natively speaking the same language.&quot; It explains why Russians exclusively speak English in video games, for example.
To make it succinct and clear: It appears that the vast majority of characters are descendants of Germans or similar races, and that they speak Japanese simply because that's the language in which the writer/creator spoke and wished to market it.

Footnotes

Note 1: Part of the Imperial House

Note 2: 東洋人【とう.よう.じん】 tōyōjin, lit. &quot;Asian people, Orientals&quot;