DSLocalizator only uses the values from the cultures that come with the dotnet framework installed in your system
There are another questions about similar problems on the DNN forums. It is a bug of the dotnet framework.
To test that you can download the snippet compiler from
http://www.sliver.com/dotnet/SnippetCompiler/
and execute the following code:
<code>
dim
a as new System.Globalization.CultureInfo("pt-PT")
msgbox(a.englishname + vbcrlf + a.displayname+ vbcrlf + a.nativename)
</code>
and you will see that nativename get the "p" using lowercase.