Ah, Noelle.  A little bit late but not to let your one topic of yours unanswered:

http://www.sk.com.br/forum/display_message.php?message_id=90897
International trade...

Foreign commerce/trade means "comércio exterior".
Sometimes, I have see foreign commerce used as opposite (or in contrast to) of domestic commerce.

International commerce and international trade means "comércio internacional", the exchange of good or services along
international borders, wich could be understood as the commerce with others countries or between two or more countries, wether involving your country or not.

I would apply the same above reasoning to domestic commerce and national commerce.

Many times it can be used interchangeably, I think.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
      Sometimes (in fixed expressions and acronyms) they can´t, as in:
      Foreign Trade Zone (FTZ)
      Ministry of Foreign trade (In UK)
      Secretary of State for Foreing Trade (in US)

      World trade Organization   (WTO).        and so on and on...