There's been several studies. The same phenomenon happens in the US among a subset of people who frame the voices in terms of older cultural narratives like, e.g., hearing the dead (i.e. traditional Western spiritualism), or with immigrants who came of age overseas. The critical elements seem to be 1) how the culture primes the person to frame the hallucinations, and 2) how family, friends, and other community members receive the claims. If both are positive or at least benign, it's less likely for the symptoms to become debilitating. Stress has a well known and very strong effect on progression of the disease. If you have angry, scary, violent voices, or when the community around you reaffirms the negativity and pathological nature of the voices, your stress levels go up tremendously.

The priming effect is huge, I think. American culture loves conspiracy theories, and conspiracy figures prominently in the experiences of American sufferers. Likewise for tropes like nefarious government surveillance, not to mention how both are infused with literal and tacit threats of extreme violence, or demands of violent responses. That's just not true to the same degree, if at all, most other places, with notable exceptions being other Anglo countries, which share similar cultural histories, not to mention sharing to a much greater degree Hollywood media which express and popularize these kinds of stories.