FISL (pronounced FIZZ lay by the locals) is a large Free and Open Source software gathering in Porto Alegre, Brazil. While the primary audience of that conference is the Latin America "libre software" community, a number of overseas speakers also participate in that conference. This is my contribution to them: a short guide for international guests visiting the Fórum Internacional do Software Livre.
Planning
Before you fly out, make sure you look up the visa requirements for your country of citizenship. Many western countries will require a visa and you will need to visit the local Brazillian embassy ahead of time to get one.
Next, have a look at the list of recommended immunizations. As with most destinations, it is recommended that your routine immunizations be up to date, but there are also other specialized ones such as Yellow Fever that are recommended by the Brazillian government. You should therefore visit a travel clinic a few weeks ahead of time.
Other than that, I suggest reading up on the country and keeping an eye on the various travel advisories.
Arrival
You will be flying at the Porto Alegre airport. If you need to exchange overseas money for Brazilian Reals, you can do that there.
You'll probably also want to pick up a power adapter at the airport if you
intend to charge your laptop while you're in the country 
Brazil has both
127V and 220V outlets using
Type N sockets.
Privacy note: using the free airport wifi will require giving your Passport details as part of the registration process.
Language
If you don't speak Portuguese, expect a few challenges since most of the people you'll meet (including taxi drivers, many airport workers, some hotel staff) won't speak English. I highly recommend getting a phrase book before you leave and printing paper maps of where you are planning to go (to show to taxi drivers when you get lost).
Native Spanish speakers seem to get by speaking Spanish to Portuguese speakers and understanding enough Portuguese to hold a conversation. I wouldn't count on it unless your Spanish is quite good though.
Also, the official conference blog posts get eventually translated to English, but there is a delay, so you may want to subscribe to the Portuguese feed and use Google Translate to keep up with FISL news before you get there.
The conference
FISL is a large conference and it has a very "decentralized" feel to it. From the outside, it looks like it's organized by an army of volunteers where everyone is taking care of some portion of it without a whole lot of top-down direction. It seems to work quite well!
What this means for you as a foreign speaker however is that you're unlikely to be provided with a lot of information or help finding your way around the conference (i.e. no "speaker liaison"). There is a separate registration desk for speakers but that's about all of the attention you'll receive before you deliver your talk. So make sure you know where to go and show up in your assigned room early to speak with the person introducing you.
If your talk is in English, it will be live-transated by an interpreter. It's therefore a good idea to speak a bit more slowly and to pause a bit more.
Other than that, the organizers make an effort to schedule an English talk in each timeslot so non-Portuguese speakers should still be able to get a lot out of the conference.
FISL was a lot of fun for me and I hope that some of these tips will help you enjoy the biggest FLOSS gathering in the southern hemisphere!
Hi, I also was invited to this years FISL and enjoyed the event a lot. Just one correction about the free Wifi at airports: They want some details - but I never gave my details. Any numbers, addresses, gender whatever they want will do. Sometimes they want to have your flight number - well, usually you can pick a random flight from the schedule in front of you. So they just gather any data, not yours.