Yes, in many non-EU countries, an IDP is a legal requirement alongside your domestic license. It translates your license into multiple languages. Japan, for instance, is extremely strict and requires an IDP issued under the 1949 Geneva Convention.
It means 'priority to the right'. Unless signs indicate otherwise (like a yellow diamond sign or a thick line on the road), traffic joining from a road on the right has priority over traffic on the main road. Be highly vigilant in rural French villages.
Generally, no. Unlike in the USA or Canada, turning right on a red light is strictly forbidden across most of Europe unless there is a specific green arrow signal pointing to the right illuminated next to the red light.
In most European countries (including France, Switzerland, and Germany), devices that actively detect or jam radar signals are completely illegal and can result in severe fines or vehicle confiscation. Even GPS systems warning of fixed camera locations must have that feature disabled in countries like France and Switzerland.