Most investors who buy international stock funds are also making a currency bet, whether they realize it or not, since the vast majority of retail oriented international funds are unhedged by default. Returns have two sources, the performance of foreign stocks in their local currency and the movement of that currency against the dollar, and the second piece can sometimes matter more than the first.  

Currency swings have historically added meaningful volatility to international equity returns without a reliable long term return premium to compensate for it, the textbook case for hedging away a risk rather than being paid to bear it.  

Hedging is not free though, and the cost has grown since US rates now sit above those in Europe and Japan, meaning dollar based investors pay rather than get paid to hedge. Safe haven currencies like the yen and Swiss franc also tend to strengthen during market stress, a diversification benefit a fully hedged portfolio would give up.  

Finsum: Before buying an international fund, checking whether it is hedged or unhedged is a small piece of diligence.