Replacing units by translated versions is not the way the Lazarus translation system works. The minimum requirement to create a Portuguese-only application is to copy the file lclstrconsts.pt_BR.po from the ide/translations folder (in your Lazarus installation) (as well as other pt_BR.po files from other packages) into your project directory and to call TranslateUnitResourceStrings for each very early, e.g. in the initialization section of the main form unit.
var
PODir: String;
initialization
PODir := Application.Location;
TranslateUnitResourceStrings('lclstrconsts', PODir + 'lclstrconsts.pt_BR.po');
See attached demo project.