Are Language Interface Packs the same as coming with the language?

A long time ago I installed Windows in English and used a Language Pack to translate to PT-PT. But it was kinda bad because certain things wouldn't be translated.

I have a MSDN account and I can only download Windows in English or PT-BR. If I download the PT-PT language pack would it be the same as downloading a PT-PT version of Windows?

Also why can I only pick those two languages in MSDN?

Thanks