Where could a lactose intolerant person eat in France?
Anywhere really. Most lactose intolerant people can eat cream and butter in the quantity used in most dishes. Ice creams sell as well in China or Japan as anywhere else really.
If that amount still poses a problem to you, most if not all restaurants certainly have dishes that do not use cream and butter or use them in an extremely limited amount, e.g. salads and steaks and many other baked meats and vegetables. They can certainly serve them without sauce if you ask. You can also ask the restaurants if they offer alternative sauces or gravies without or with less butter and cream.
If you have problem with even sautéing with butter or a tablespoon of heavy cream though, that’s way beyond the lactose intolerant category.
Of course, international chain restaurants (McDonald’s) and “ethnic” restaurants or stands (Chinese, African, Turkish, etc.) are also not hard to find in cities.
If you have a very strong reaction to lactose, or an allergy to diary products (which are rarely caused by lactose but by certain proteins), where mere presence of lactose or dairy products poses a significant issue for you, you need to cook yourself or individually verify with specific restaurants. Like for all other severe allergies, you cannot trust others on cross-contamination based on type of restaurants alone, especially if there is language barriers.