Okay, folks... here's a good discussion topic for you;
Racial languages/religions/alignments.
I personally really dislike the "homogenous" races idea which seems to be present in a lot of TTRPGs, (D&D in particular).
First, forget touching on elves or dwarves for now. Everything you say about racial homogeneity in fantasy worlds tends to apply to humans first, and humans are a much easier standard.
I once thought many of the same things you think here. Before you grumble too much, I suggest you play without nigh universal languages for a few years and the come back and report your experiences.
Widespread linga franca do exist but often not as mother tongues in the real world. Nonetheless, a very limited number of languages has a nigh invaluable benefit to an RPG because its just not fun having a cool RPG that you can't RP with because of a lack of a common language, nor is it fun to have hints and clues in languages the players have no chance of reading. Simplified language choices help games from D&D to Call of Cthulhu.
So whether you have a hard time believing everyone grew up speaking Latin or a handful of other tongues, it really is helpful for your RPG to work that way.
As for cultural diversity, it's very difficult to create sufficient unique cultural artifacts to invent cultures whole cloth, and D&D has typically not focused strongly on cultural norms or when it has, it's taken the easy way out and applied a stereotypical trope culture like 'Ancient Egyptian' to a nation and made a nation on the map a pastiche Egypt, Viking, Chinese, Russian, English, or whatever. So since none of the human cultures on the map tend to have a lot of cultural depth, there is little reason to imagine anyone is going to be particularly adept and inventing cultural depth for demihumans in the setting as well. Generally you have to be satisfied or even impressed when anything in a setting shows some real cultural or social imagination. Asking for two cultures in the same setting to have a lot of depth is perhaps asking too much.
Beyond that, most people are incapable of imagining cultural norms much different than their own unless they've also grown up in multiple places with different cultural norms. So one problem with emphasizing really imaginative cultural norms is you quickly create a setting where none of the players can successfully roleplay a character from that setting because there is this huge overhead of cultural IQ that they have to acquire first, probably through play, and for many of them it will be a bridge too far.
I don't really have a problem with an entire race having the same moral compass, particularly from the perspective of a human looking in and not necessarily seeing all the shades of difference that are there. I suspect in fact that humans as a race tend to have a pretty similar moral compass, even if they are notoriously bad at following the one that they generally agree that they ought to have. It doesn't strike me as surprising that a different species of being would on aggregate or average show a different system of mores than people do, or that cultures (whether human or not) could on aggregate or on average have different sets of values. So for example imagining that dwarves cooperate and hold group values with greater weight than all but the most lawful minded human civilizations doesn't strike me as anything but likely, whether we are talking about 'evolved from a different animal species' or 'created by a different creator', my expectation is a lack of distinction would be surprising rather than the reverse.
Religion is much the same way. I rarely encounter anything like a well thought out religion anyway, and rarely do RPG authors really want to investigate religion in any sort of deep manner. If a setting has even one interesting religious take, that's a positive. Asking for several might be asking more than is reasonable.
As for alignment, I don't really know what you mean. They've never been particularly mechanical. They are I think a bit overly simplistic but they might just be complex enough for the purposes and anything more complicated is likely to be vague to the point of being meaningless, or else actually "mechanical". And I confess I have a bias. Everyone whom I've ever played with who told me that Alignment was too simplistic to capture real human morality has played their PC in Pawn Stance, and their actual problem with Alignment seemed to be that it's existence nagged them away from their preferred Pawn Stance play.
I'm going to apologize for being a bit tightlipped with actual examples of cultures from my homebrew world, as I'm protective of my ideas. My world is unapologetically homo-centric, because I think it's so difficult to relate to a non-human perspective that if I made a non-human perspective default I'd be making it too hard for players to thrive in a social setting (in setting). But I do try to have cultural differences. Sometimes those cultural differences you have to paint with a pretty broad brush just to get them across, because you rarely have the time to invest in anything other than broad stereotypes - a few sentences to convey to a player recognizable features. But that's more the nature of the medium than it is any commentary on the fictional cultures, and it's certainly intended that if you investigated you'd find a lot of diversity within the individuals from that culture.
