There are three main things you should take in mind when localizing your website, game or app for the Latin American market, including Brazil.
First of all, make room for longer strings. Spanish and Portuguese texts tend to be 10-20% longer than their English counterparts. Even single words can be twice as long than their English counterparts.
Noun gender variation
If you are concatenating strings and using placeholders, make sure your code can handle variations for variations in noun gender (masculine/feminine) and number (singular/plural). One adjective or passive verb in English can lead to 4 different translations. For example:
English original: “%s updated”
“%s atualizado” (singular, masculine)
“%s atualizada” (singular, feminine)
“%s atualizados” (plural, masculine)
“%s atualizadas” (plural, feminine)
Date and number format
When dealing with numbers, use the metric system for this region, as well as the date format DD/MM/YYYY. If you are using code to write numbers with words and are dealing with really large figures, take into account that some countries use the short scale, while others use the long scale. Brazil uses the short scale just like US. However, most of Spanish-speaking Latin American countries, like European ones, use the long scale. For more information on short and long scales, check this article from Wikipedia.