Do you know any French? Do you know a romance language (Spanish, Portuguese, Italian) or Latin? Have you lived on your own before, or largely independently, or done boarding school? Do you have any recent experience living in a foreign country? If the answer is no to all of these, then I would not recommend the Berkeley/Sciences Po program.
Moving away from home is a big transition for almost everyone. Adjusting to college coursework is a big transition for most people. Creating a new social circle is also a big transition. Those are all going to be hard enough in a language in which you are fluent and in an academic style that will generally be familiar. Trying to do all of those things in a country where you don’t speak the language and the educational system is very different is going to be an even bigger challenge.
If you are still really interested in the Sciences Po program, find out from Cal how the grades transfer. If it’s like a typical French university, they grade on a 20-point scale. 20 is for God, 19 for the professor, and 18 for the best student in the class, maybe. If Berkeley is doing straight conversions (i.e. 18/20 is 90%) then your college GPA could really be in shambles. Most American universities doing exchange programs have a more generous conversion rate (I think 14/20 converted to an “A” back in the day for my college).
As far as the W colleges, I don’t have a strong sense pushing towards one or the other in terms of academics. But just from what you’ve said here, I have a strong inclination towards Williams for you. Why?
The summer program is going to help you become familiar with the campus, campus life, professors, help meet friends and build your social circle, etc. That way, when regular classes start, you’re already a couple steps ahead of the game. And they’re giving you stipends for summer research/internships. Oftentimes some of the best internships in terms of experience are unpaid. Getting a stipend is golden. Free textbooks is also worth thousands of dollars over the course of your college career. One less thing to worry about or pay for.
Frankly, it sounds as though Williams is doing everything possible to set you up for success AT Williams and BEYOND Williams. Thus, based on what you’ve said, I’d be going there. Williams is one of the top liberal arts colleges in the country and has an excellent reputation with grad schools, employers, and politicians. It will in no way, shape, or form hold you back.