The hardcoded languages have the problem that the native name is not shown, so we're left to guess what they mean in games that use the language names rather than flags or the unhelpful English names. Here's a listing of what we currently have hardcoded, the languages living as tags can have the native name listed as synonym so I won't bother with them here. Hopefully these are properly capitalized as well for each individual language.
Chinese — 汉语 / 漢語 (hànyǔ), 华语 / 華語 (huáyǔ), 中文 (zhōngwén)
Czech — Čeština
Danish — dansk
Dutch — Nederlands
Finnish — suomi
French — français
Hebrew — עִבְרִית (‘Ivrit / Ivri't)
German — Deutsch
Italian — italiano / lingua italiana
Japanese — 日本語 / にほんご (nihongo)
North Korean — 한국어 (hangugeo)
South Korean — 조선말 (chosŏnmal)
Polish — język polski / polszczyzna
Portuguese — português
Russian — русский язык (russkiy yazyk)
Spanish — español
Swedish — svenska
Spanish has many major dialects which are treated separately of the generic Spanish language by their speakers, so I guess we should too. They often are named without the español part as well (e.g. castellano), so more reason for it.
Chinese is split into Cantonese and Mandarin (spoken only? I'm not sure if these have any effect to the written Chinese language). The written form is split into simplified and traditional. In addition to many(?) dialects of it spoken outside of China.
I'd actually like to see a separation of written and spoken languages in games, but that's probably hard to implement in any manner (I can only think of very hackish solutions), so comments about the available languages should be used if they aren't straightforward though even then it should probably be noted so others will know it for certain (assumption is the root of being misinformed :b).
Similarly games with no text beyond the simple UI and no speech of any kind (not even the screeches about power ups) should have something to identify them.
If the purpose of having the native name listed eludes you, then see the following image depicting the language choices in a game...
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