Trickle vents are a shitty UK solution to enable builders to avoid building houses properly. A modern double (or triple) glazed window, with high quality seals, and then effectively a small hole is deliberately added. Nowhere else in the world does it that I”m aware of.
The *right* solution is to control the ventilation – ie make the house properly airtight and have a heat recovery ventilation unit that puts air into every room (and extracts from those that create moisture) at a set level.
The traditional European solution is to ventilate the house properly each day by opening the windows. I wonder whether it works as well in our damp climate as it does in cold dry Northern Europe?