Well, this is gonna be a doozy... this might be multiple posts, and I'm rate-limited, so we'll see...
Let's start with Chinese food...
There are multiple places here that can easily be called Chinatowns, the bigger ones being the one in Richardson on Greenville between Arapaho and Belt Line/Main and the one in Plano at Park & Coit. Lots and lots of good restaurants in both places, and the one at Park & Coit has a lot of non-Chinese Asian places too (like a fantastic Korean fried chicken place called BBQ Chicken). Any place with "Sichuan" in the name is going to be a banger; Sichuan King (now merged with Royal Sichuan, and I think the restaurant carries both names) is one of my favorite places to order ma po tofu. One of the more famous places in Richardson Chinatown is called Jeng Chi, they were one of the restaurants that introduced xiaolongbao (soup dumplings) to Dallas though they've kinda let their fame go to their head lately (they're kinda expensive now, and other places are better) though they're still pretty good. Canton's another decent place, some of the best chow fun and Hong Kong-style wonton soup in Dallas. One of the few Hunan restaurants in Dallas, Hunan Bistro, is at the Plano Chinatown, right next door to another Sichuan place. Plano Chinatown also has a decent hot pot place, called Chubby Cattle.
Of course, there are lots of Chinese restaurants that aren't in the Chinatowns. First Chinese BBQ is a local chain with locations all over town... they used to be cash-only but i understand they started taking card very recently. Fat Ni at Spring Creek & 75 in Plano serves Chinese street food, mostly on skewers—I recommend their vegetarian stuff, such as their fried gluten and tofu (yes, fried gluten on a stick, it's good). Sichuan Folk at Spring Creek & K in Plano is another fantastic Sichuan place (there are a ton of other great Sichuan places all over Dallas too). Wu Wei Din at 15th and Independence in Plano specializes in Taiwanese food. I'm fond of Tian Tian at Preston & Frankford in Far North Dallas, which has a huge menu including Peking Duck and gold and silver buns. We also have some wonderful hot pot places, Happy Lamb at Legacy & 75 in Plano being one of my favorites. My current favorite place to order from is Long Time Ago at Coit & Belt Line in Richardson, they have a huge and diverse menu with a huge selection of Sichuan dishes and Cantonese food like BBQ pork fried rice.
Next, on to Japanese food. We have an actual sushi buffet here, Osaka on Belt Line & Midway in Addison (we used to have more, but this is the only one left). We have lots and lots of ramen joints that also serve other things including some great takoyaki and curry rice: Ramen Hakata at Belt Line & Marsh in Addison, Higuma Ramen & Izakaya at Belt Line and Midway again (different corner from Osaka though), Monta Ramen at Coit & Arapaho in Richardson, and several Yama Izakaya & Sushi locations all over town. We have an actual Japanese supermarket, Mitsuwa Marketplace, at Legacy & 75 in Plano, which has a food court inside full of great places. Gyu-Kaku is a chain of yakiniku restaurants (with an all-you-can-eat option) and locations in both Addison (Belt Line & Montfort) and Plano (Preston & Headquarters).
Korean food... our main Koreatowns are at Old Denton Road & Trinity Mills in Carrollton and Royal Lane & I-35E in Northwest Dallas. I've only been to the one in Carrollton, but it's amazing. Korean barbecue (some of which are all you can eat!), Korean fried chicken, Korean bakeries, Korean shaved ice places for dessert... the centerpiece of it all is H-Mart, a giant Korean supermarket with a wonderful food court inside. Everything in that food court is fantastic, and they serve food from several other Asian countries too, including my favorite place for xiaolongbao in Dallas. But their actual Korean food in the food court is fantastic too, there's one place that seves bulgogi in stone bowls and amazing sundubu (tofu soup). There are also a number of Korean fried chicken places outside the Koreatowns, including a number of BBQ Chicken franches all over and Bonchon Chicken at Belt Line and Quorum in Addison.
Thai food... we have Thai restaurants all over. Admittedly, I'm not familiar with the breadth of them because I've usually stuck to my favorites because they're so good. Banana Leaf at Preston & Campbell and Thai Spice at Frankford & the Tollway, both in Far North Dallas, are fantastic and I always find myself going to one of those two when I want Thai food (keep in mind: Thai Spice lives up to its name... I can handle spicy food really damn well normally, but I got a 4 on their menu once and it was too much for me, I've been told by friends that their food is usually one or two levels spicier than other restaurants at the same number). Plenty of other good places, I'm just a bit set in my ways here.
Vietnamese food... oh we have a ton of them. Lots and lots of pho places, just search Google Maps for any restaurant with "Pho" in its name and you'll find something fantastic. The best places are the holes-in-the-wall with no decor. My go-tos are Pho Pasteur II at Belt Line & Josey in Carrollton and Pho Truong at Arapaho & Custer in Richardson. I have to admit I haven't gone for pho much lately... thanks to the pandemic I've mostly just been ordering delivery with a few exceptions, and pho doesn't deliver well. But it's still good, and I'm starting to go out to eat again so hopefully I should be eating more pho.
...and I think I'm going to take a break before typing out any more. I'm sure I'm rubbing up against a character limit anyway, and I want to get this submitted now in case my machine eats this post. I'll write up some stuff about food from India, Nepal, West and East Africa, various parts of Latin America, other regional American cuisines, etc. later.