Missionaries going to France can expect mild, temperate weather for most of the year. Coastal France is very wet (both Brest and Lorient boast around 300 days of precipitation a year). Paris, in contrast, is fairly dry, although "Springtime in Paris" usually brings a fair amount of rain. Missionaries are well-advised to have rain gear for such conditions.
Mid-winter temperatures can get below freezing and mid-summer temperatures may exceed 30°C (86°F), but year-round, the average is in the low teens.
Bring a warm, waterproof overcoat, a couple of pairs of long underwear, and some warm wool socks for the winter. Through about half of the year, you won't need to wear a suit coat, so bring a few pairs of dress pants (not Dockers) so you can save the suit pants for the winter and Sunday. Make sure the pants are of a durable fabric that will wear well when riding bikes.