Going to Seoul Korea for my brothers wedding in July and I'm not sure how to dress.?

It is a formal Korean wedding. Traditions? Food? Dancing? Weather in July? Things I NEED to know. My bro taught there for a few years and speaks Korean like a Korean. I also need to know if I'm going to be completely lost not knowing the language. Should I start learning now?

About the language, you'll be fine. Just learn how to bow instead of handshakes, since you'll be introduced to many many people.
Formal Korean wedding is in four part. First, "western" style, bride in wedding gown but not quite dramatic as real western wedding. We don't stand when bride comes in, no kiss, all the small details are not there.
After the ceremony, it's picture time. Just listen to the photographer. (You'll be one of the first group to take picture, so pay attention when to show up)
Third part is traditional part, I'm not sure if they'll include it or not - since... family of the groom plays a lot of part here, and your not native Korean, so... discus with your new sister in law. It's called "韽愲氨" (cut and paste these letters, she'll know what you mean)
Fourth part is reception. Usually you may need a ticket to enter the reception place, and they give you ticket before the ceremony. It's just eating, no dancing. Stay close to someone you know, grab a seat and eat your food.

No! Hey speak english. And in every taxi they have free translators. They also have free guides. Check travelkorea.com.

I'm Korean. First of all, korean weddings are kinda different. People talk, eat, exit and enter in the middle. They still wear tuxedos and a white dress. However, there aren't traditional groomsmen and bridesmaids. They also bow to the parents and pose for a big group picture afterwards. They usually have an MC who narrates things too. All said, it only lasts about a half hour.

Just wear something you would to a normal american wedding: not jeans and tshirt. Just very nice casual or a little dressy.

Weather in July is freaking hot! It's monsoon season there and it is damn Humid! If you're a woman, wear a type of summer dress maybe.

Most young people CAN speak english, but choose not to. While there are not many foreigners there, people aren't surprised and will speak to you in English. Subways are in english too. If it's in Seoul, you'll be fine.