Cloths during trevelling in Mid of Septermber in Paris, Swiss

Where are you from and where in particular are you going? I've traveled to France at exactly that time and also Basel, Switzerland. It was quite warm. We wore summer clothes. It was 90degreesF in Basel. We did get some rain in Paris at that time. You should bring a rain coat.

And at what elevations? Makes a difference.

Your best bet is to check a 10 day forecast a few days before you leave for Paris and Wengen (your two locations) and pack for those temperatures. Plan on taking layers. Depending on the temperatures closer to your arrival time and elevation in Switzerland you may need a “jacket” of some sort. Still too early to tell now.

If you're taking the lifts up to Jungfrauoch or Schilthorn, it can be chillier at the top. Carrying a packable waterproof jacket can also be a good idea (and we needed it in September on one damp day in Mürren -- took the train to Lauterbrennen and saw the internal waterfalls.)

I was in Paris, Lyon, Annecy, Chamonix then down to Provence and the Riviera last September (2017). I typically pack at least one warm layer and a rain shell that I can add over a tee shirt and button up shirt to keep me comfortable down to fairly low temperatures. Because I was going to the mountains, I packed two warm items, a lightweight wool sweater and a packable down vest. I also packed some light gloves (runners gloves for winter) and a light ski cap. I didn't pack any long underwear or wool socks. I survived up on Mt. Blanc but I wasn't warm. A little heavier ski cap, wool socks and some silk long underwear on my legs would have helped a lot. I've now ditched the packable vest and gone to a thin down jacket (sometimes referred to as a down sweater). I decided it's not much extra weight or bulk and gives me a second legitimate outerwear choice on dry, cool fall evenings.