You have a number of topics within your question, so let's focus on the titled question - the sexist environment.
I won't even attempt to tell you that I understand what you, personally, are dealing as I am looking at this from the perspective of a) a male, and b) an American. However, I can empathize and I most sincerely do.
Male interviewers staring at my boobs and stealing glances when I am
answering.
If you are catching them, they are obviously oblivious to the fact that they are being not only rude, but disgusting. While you can't stop them from looking, you can catch their attention by asking a complex follow up question.
You need something to break their (lack of) train of thought and engaging people in a dialog is one sure way to do that. Also ensure that you keep good eye contact. If they are stealing glances, they know on some level what they are doing is wrong. Strong, but not aggressive eye contact (subconsciously) lets them know that you are aware of their gaze.
Some of the interviewers ask me to explain something on the board and
while I am doing so, they tend to stare at my ass. And again, steal
glances.
Unfortunately, until we actually have eyes in the back of our heads, we can't see what others do. However, you can mitigate some of this by positioning yourself at an angle to the board as you write. In other words, don't stand perpendicular to the board. Look back to the audience (more) often. It won't stop them, but it will also communicate that they may be caught being rude.
Some advice...
Dressing "appropriately" is subjective. Dress for the position you want not the one you are applying for. In other words, if you want to be a VP, dress like a VP.
Never let them see you coming (American expression). You said that you spoke up to 3 languages. Don't let them know this unless it's a requirement. If the derision is something you can tolerate, it's better to get information than to get insulted.
Remember, in the 1980s and 1990s Japanese businessmen understood English whereas their American counterparts didn't understand Japanese. The Americans foolishly spoke openly about their positions while the Japanese pretended to not understand. It gave them a huge advantage while negotiating.
Bottom line: while it may be a "social victory" to get these males to change, it's unlikely you're going to do it overnight and by yourself. In the meantime use their foolishness to your advantage.
