imperfection

“The man who finds his country sweet is only a raw beginner; the man for whom each country is as his own is already strong; but only the man for whom the whole world is as a foreign country is perfect” (Todorov 250). Is this correct?

Yes.

I think that Todorov expresses the need to openly experience other cultures exactly.
For those who are satisfied with their own country and do not thirst to learn about others' do not know what they are missing out on. They may think that they are happy with what they have, but they clearly have little experience; upon visiting another country - with an open mind - one finds something that they like better about that country/culture than their own. They are beginners who think only of themselves and have not considered what others are like. This inherently makes them imperfect as their eyes are not open to the world. With travel and experience, they may move past this beginner phase and enjoy other countries as well as their own.
For those who are comfortable in every country lack an outsiders' curiosity. They are at home no matter where they are, accepting all country's cultures and learning to fit in with each of them. This, however, prevents them from looking at a culture with an objective view. It is difficult for them to learn more about the culture when they are a part of it. You may be strong and know many different things, but with comfortability, comes a lack of curiosity; when you're comfortable, you stop asking questions and thus stop learning more about the country that you are a part of - making you imperfect.
For those who view the world through a crystal ball, who learn about other countries without claiming them as their own, who observe cultures as if they are foreign, no matter how much they already know about them, they are curious, learning, yet strong in their knowledge so that they could fit into a country if need be (without becoming a part of the country). They are perfect. They are also nonexistent. No person can view all countries like a foreigner, with no ties to any of them. While people may strive to reach this state, to look at the world objectively, taking in as much information as possible, they simply cannot always do it.
Cortes is, too, condemned to this imperfection. I agree with Rebecca, that of these three categories, he would fall under the second, that of a strong man; he often compared the Native Americans and their culture to the Spanish culture, explaining similarities and differences. He seemed to understand their culture as well as Spanish culture and thus was stronger for it.