I know nothing about the subject and what the jargon and "stock phrases" might be, but going purely on logic alone:

1) Taking out the qualifying clause, we have "The
internationalization theories are often called the economic approach." I don't see how theories can be an approach. Things are not a process. Something more like "Theorizing on internationalization is often called the economic approach."
It seems unlikely like that "the economic approach" consists of all possible "internationalization theories focusing on
multinational companies" which I think the sentence could imply.

2) Depends on your meaning: viable, feasible, valuable?

3) Let's substitute some words: The purpose of a story is not to summarize itself. Tautology. That's not a very informative statement. As far as "good", are "good theoretical statements" good in theory or good in practice? What kind of good, i.e. would just changing good to something more specific help?

4) Is there more than one kind of "good knowledge"? Every stage involves six good knowledges of ... Again good is vague. And is there more than one international business environment? Would "involves in-depth knowledge of the international business environment" be better?