Remember that cultures in your game are really only different if they are different to the players. Cuisine is a distinct cultural element in the real world, but it's not guaranteed to be noticed by your players; they might not look at the menu in the restaurant, and even those who do might not notice what's unique about it.
In order to make cultures differ in the eyes of the players, there are two approaches you can take:
- Choose a cultural difference and design an adventure around it, or
- Design an adventure and then derive a cultural difference from it.
The two approaches have the same goal: Making cultural differences important enough to the players that they cannot avoid noticing them.
As an example of the first approach, let's continue with the idea of cuisines as important cultural differences. How can we make this relevant to an adventure so that they players are sure to notice it? We could invite the PCs to a banquet in a foreign land where an assassin kills important figures using poisons and ingredients unique to that land. Solving the mystery requires a thorough look at the banquet's menu, rummaging through the kitchen, and learning about the peculiarities of the nation's cuisine.
The second approach is the reverse of the first, so we start with the adventure and try to extract a cultural difference from it. Let's say the party is searching for a wizard in a foreign land. We could make the culture of this nation very hostile towards wizards, which will make the search more challenging: Some will refuse to help because they are afraid of arcane magic, others will tell the authorities about a hidden wizard operating in the land, and a few might even become hostile toward the PCs for asking.
In both cases, the players are guaranteed to pick up on the cultural difference because they're important to the adventure itself. This can in turn prompt the players to find out about other cultural differences, including those that might not have an impact on the adventure.