My opinion, for what it's worth...
As I said in an earlier discussion of this subject, I wouldn't invest a penny inside China (the PRC). I don't trust them at all. I have similar feelings about Viet Nam.
I do, however, have a small amount in Matthews Asian Growth and Income fund (MACSX), which invests in companies outside of China that sell into China. This is the closest I come to a single-country play and it only gets a small slice of the pot. (Metaphors aren't my speciality.
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Brat recommended a fund for India that has done well. I have better feelings about direct investment inside India. Same with Brazil. However, so far I am letting Vanguard take care of other emerging markets for me.
For a long time now I have had half of my equities in international funds (index funds except for MACSX)--mostly Vanguard's Total International Stock Index Fund, but some in their Emerging Markets Index Fund. This mix has done very well for me so far. I made this 50/50 choice after reading Les Antman and Paul Merriman
FundAdvice.com - Articles who provided historical information supporting it. Scot Burns suggests his Margarita Portfolio which has 1/3 in total international and Bill Bernstein,
Efficient Frontier , has shown graphically with the best historical data how adding international reduces volatility and can improve returns over time. Not everyone agrees with this idea and many won't touch foreign companies, Including John P. Greaney, my patron saint.