1) 'The country is part of the G-20' is how to write it. The G-20 is exclusive and only contains 20 countries so therefore you are talking about a specific country, it isn't right to use 'a' unless you were being hypothetical e.g. 'If a country were part of the G-20' 2) 'Korean culture' for the general culture of the country 3) Again you are talking about society in general, so you don't need 'the' X has an impact on Korean society. 4) Here you need 'the' because you are talking about something specific affecting the Korean culture and language The foundations of Korean culture and language...

1. Would be "The country is a part of G-20" or "A country is part of G-20" 2. It's not necessary to use "The" here but if you did it would not be wrong 3. Same as above, you could write "Globalization has an impact on Korean society" or "Globalization has an impact on Korean society" both are correct 4. This one is kind of tricky, if you were talking about "The Foundations of Korean culture and language" you would use 'the' and "Foundations of Korean culture and language" could be the name of something like a University course or something, but when talking about it you would need "The Foundations of Korean culture and language"