I'm new to mac development and I don't know how to localize the sparkle dialogs to brazilian portuguese. I looked the files pt_BR.lproj, but i don't know how to configure.
What do i need to do?
You'll probably have to edit the Sparkle project, add the localization you want (In Xcode, choose the project file in the project navigator, then select the project, not the target, and add the localization in the info pane).
Then proceed as usual and translate strings that appear in the different NIB files.
Why will i have to edit the source code, if the project have the pt_BR localization?
You won't. I imagine localized stuff reside in XIB, and strings files for the most part. This is also simple to verify.