I am making a human only campaign, and I want to make human subraces that emulate real world cultures. I am looking for subraces for Chinese, European, Indian, African, Mexican, Russian, Eskimo, and Native American people. Thank you in advance!

Other than custom language, I don't really see the point in making subraces for these. I should mention the standard Forgotten Realms has its own equivalent of humans that have regional differences with those that take after Norse, Egypt, Orient, etc. Basically beyond physical description and typical names nothing is different. So, from a purely mechanical point of view, there's no point to subraces for what you're asking about.

A lot of the differences between people of different regions is more about background. For instance, Native Americans would be more inclined to an Outlander background as they are a tribal culture heavily favouring forest and woodland. Beyond that culture, however, a Native American is not really any different than somebody born in a city, or in Japan or anywhere. A human is a human no matter the region born in. You seem to be confusing "race" and "culture". A race is something you are no matter where born or what culture born into. The variations of humanity are already covered by the racial traits offered of Human and Variant Human. Even regional adaptation isn't some genetic thing. Eskimo are suited to cold environments, yes, but they have no actual biological advantage in this. If you went to those cold regions and lived there then after a while you'll become equally acclimated as they are. Humans are naturally adaptive in this regard - that adaptability and our intelligence are the only reasons why humans have survived and why we are so widespread. It would therefore be silly to give a feature of cold resistance or something similar to Mountainborn feature of Goliaths. Humans don't have acclimation on that scale for such features - you could be an Eskimo and lived in the cold your whole life as did all the generations before you but if you go swimming in a icy lake you will get hypothermia and die like any human would. An eskimo has no biological advantage against the cold - they just learned how to keep warm in those environments like through furs, fires and shelters. That's not a racial thing.

Still, while I strongly dislike your idea it is possible for you to make an Eskimo with such a feature if you feel it necessary. But frankly you'd have to lose some of that versatility and will probably have a hard time balancing/justifying that to players. Trying to find such for all the various regions will also be incredibly difficult. And to then try and do this without falling into insulting racial stereotypes... Yeah, you're just making a huge amount of unnecessary work.

Personally, in an all-human campaign I'd not bother with all that and just say they could take variant. The variant human with ability to choose skill proficiency and a feat and choosing which stats to increase plus a language is covering all bases already. It does all the work for you (which is why the human race as given in the write up already details regional variation as "fluff" not a stat/mechanic thing). Or, if you really wanted, go the "Variant Tiefling" route where instead of a skill proficiency they could take a weapon/tool proficiency and instead of a feat they could take damage resistance or something. All you need. The players being able to choose what suits them is better than shoe-horning them into a choice by "regional" things like being Russian or something similarly trivial (as far as game mechanics should go).

Oh. Right. I totally forgot that variant human existed! D'oh!

I totally could just use that, thanks!

I have a homebrew variant called wild human that is pretty good. 3 of my players use it. Could be what you’re looking for.. link is below

Personally for variant human cultures I use the Variant human option but have those options set to specific things or an option between a few possibilities (just like variants of other races do).

For example a culture similar to the Norse, for ability scores I give them +1 Constitution (as a typically hardy folk) and the option of +1 to Strength or Charisma (they love their fighting and revelry).  While for the variant skill they have the option for one of the following Athletics, Survival, Smiths tools or Carpentry tools (key aspects of the culture that get taught to everyone of that culture).

This still lets character have whatever background that may suit their character concept, but still ties them back to their initial culture (eg. a Nordic merchant, sailor or mercenary).

A thing to keep in mind is despite the other races getting additional ability score bonuses or skills, their natural potential is much the same as any other race (a max of 20) should they put the effort into getting there.  While the term race is often used in place of species for D&D because it is tradition.