I live in France. I saw topless women at the beach this summer, and by the pool area. Not many, but some, so it’s still done.
YANBU however for being pissed off at her being topless; I wouldn’t like it either.
YABU for expecting her to speak English to your DH. He works in a French office; they’ll be speaking French to each other all day long. She spoke to you in English, yes? So she already made that effort for you.
YABVU for calling her a slut.
By all means speak to your DH and explain how it made you feel uncomfortable. Do not approach his colleague; you’ll be laughed at, and make your DH’s position in his new job very awkward. Right now, both you and he need friends. I suggest you look for your tribe, perhaps on local English-language Facebook groups.
As someone said up above, moving to a different country and language is hard, especially for the trailing spouse (not a nice term, but for many of us, that’s what we are). For those of us with kids in the mix, we also have to navigate schools, their emotions etc.
Do you work? As a SAHM, my job, as far as I saw it, was and is to support my DH by creating our home and social life. Not sure whereabouts you are (sounds like south or Atlantic coast, if you’re by the beach), but there will be resources available to you. France is a great country to live in, but you need to start with an open mindset.