I’m moving to Montgomery, Alabama for a year from Sweden. Anything I should know?
It's going to be a culture shock coming from Sweden. BIG difference. I'm actually wondering if you'd be ahead compared to other students your age. Have the school do a placement test to make sure they put you where you'd be most comfortable.
Some ideas on things to do, depending on your budget/ability…
Attend the Iron Bowl. Stephen Fry's reaction to it has stuck with me, and I feel like those not from the US would really be in awe of it.
Make sure you get in a trip to the beach at some point. Alabama has gorgeous beaches. Huntsville's Space and Rocket Center, Birmingham's multicultural scene and Civil Rights museum, and Mobile's Mardi Gras are all worth checking out.
Surrounding states aren't a bad drive away. Florida, Tennessee, and Georgia have a lot of things to explore. With you being this close to Walt Disney World and Universal Studios, it's worth it to take the opportunity if you can afford it. (I don't know what your budget allows.)
Flora… Poison ivy/oak are the two big ones to avoid. It's not a huge issue if you're in a suburban area, but if you go into the woods, be aware.
Fauna… Lots of deer in the right areas. Raccoons and armadillos. Large birds of prey. Frogs. Turtles. They'll leave most humans alone, but watch out when driving at night. Watch out for snakes when in any tall grass or near water.
Love bugs are a twice a year thing and annoying but harmless. Gnats (fruit flies) are also annoying. Avoid leaving out fruit and potatoes, as those will attract them indoors.
Mosquitos, ticks, and fire ants are the biggest issue here. Don't leave standing water sitting out, to avoid mosquitos breeding. Wear insect repellant when going outside. For ticks, make sure you're as covered as possible when in long grass or a heavily wooded area, and be sure to check yourself and have someone else check you when you're done. Fire ants are nasty buggers who build mounds all over. Just look out for ants. You'll know if you're bitten by one. It's right in the name.
Heat… That's going to take some getting used to, for someone from a much cooler climate. Most homes here have air conditioning, so take advantage. If you must go outside, early mornings and evenings are of course the coolest. Sunscreen is a must to prevent sunburn, but that is pretty universal. Light fabrics are good. Sundresses and shorts are popular during summer months for a reason. Carry water around with you and stay hydrated. A pocket fan/mister is also nice. We have a lot of popular cold foods and drinks down here, too.
Tornado season… I can't stress enough how important it is to read up on tornado safety and to be prepared. This is typically March through May, but we have the occasional outlier.