Hi Rod,
Basically the way it works by default is that the executing thread will be set to the language preference of the browser and this causes the use of the preferred language resources files. However, it seems that many or most people don't know about the browser settings for language so its possible many users have en-US as the browser language even though they would prefer pt-BR.
It is possible in mojoPortal to force the use of a particular language instead of relying on the browser preference, this is documented on the bottom of the page here:
http://www.mojoportal.com/localization.aspx
So, if you wanted to force the use of pt-BR you could make settings in Web.config/user.config like this:
<add key="UseCultureOverride" value="true" />
<add key="site1culture" value="pt-BR" />
What this will do is cause the executing thread to use pt-BR instead of the browser preference so that by default the pt-BR resources will be used for all requests. It will still fall back to English for missing keys in the pt-BR resources as it should.
Note that site1culture is for siteid = 1, so in a multi site installation you can set different languages on different sites based on siteid, so the key for siteid = 2 will be site2culture and so on.
Hope it helps,
Joe