English is the de facto language of international relations, more so than any other language anyway. And English is also the working language of ICANN, IETF, and any other technical body dealing with the Internet I can think of.
Point is, the fact that slightly different words are used in Spanish and Portuguese really doesn't matter. They might also want those words as well, but they have claim over the English version too. For example, even though the word for Japan in Japanese isn't "Japan", ICANN would never delegate that TLD to anyone else besides the Japanese government (and indeed even that TLD would be unlikely to be created because it's redundant with the .jp ccTLD).
Point is, the fact that slightly different words are used in Spanish and Portuguese really doesn't matter. They might also want those words as well, but they have claim over the English version too. For example, even though the word for Japan in Japanese isn't "Japan", ICANN would never delegate that TLD to anyone else besides the Japanese government (and indeed even that TLD would be unlikely to be created because it's redundant with the .jp ccTLD).