The Thai one is usually a bottled one you can buy at any Asian market, and is just sugar, water and chili cooked down to a syrup. start with the amount of sugar you want for the final sauce, at an equal part water, a few smashed garlic cloves and a lot of fresh thai chili (it will get less spicy when it cooks down) Reduce it until it's the original volume.
the Vietnamese one (nuoc cham) is usually thinner i found this recipe-
4 red chilies
2 cloves garlic
1 tsp sugar
2 limes, peeled and chopped
1 tbsp hot water
1 tbsp vinegar
5 tbsp nuoc mam (fish sauce)