On testing a design.
Design and UX design face the issue of intuitiveness and knowledge. The intuitiveness is something done by intuition. Intuition depends on knowledge. So what comes as intuitive to a young Japanese girl could not be intuitive at all for a young American girl. But there are universal norms based on common knowledge that most people around the world would understand. It is not universal in the way a baby without any cultural immersion could understand. But it is natural because societies often follow the same paths.
Think about the emojis: a lot of them are interpreted the same way all over the world. The same for the color red in interactive design is associated with a "not this way", "stop" or "the end", as the opposite of the color green.
It doesn't mean we just need to focus on what is universal, but it means that universality is a good frame for specificity. If it is the first time you use a phone in China, which is set to Mandarin, answering a phone call will be easy. But finding a way to record the conversation with the same phone could require a learning phase.
Designing an app interface could follow these steps: create a frame or first layer that almost everyone should understand, then add functions that your users will understand. It will create a comfy mindset for every user. How to design this first layer? Put down some ideas and just ask grandma.