International stock mutual funds outperformed the U.S. stock market for much of the past 10 years. But international funds fell behind in the past year amid difficulties in stimulating moribund economies in Europe and China as well as Greece’s debt problems. A $10,000 investment in the average international fund on June 30, 2005, would have grown to $18,825 by Aug. 4 this year, according to Morningstar Inc. data.