1. "与美国医学生不同，外国医学院毕业生需要三步都通过才能申请做实习医生": wrong, FMGs only need to pass USMLE Step 1, Step 2CS & Step 2CK to be certified by ECFMG, and with the ECFMG certificate, you are good to apply & do US residency.
2. "第三步主要考怎样把所学知识用于临床，涉及与病人交流，国内很多医学生因为语言问题都在这一关被卡住了": this is not Step 3, it shall be Step 2 CS (clinical skill), it is right that many chinese guys fail with CS, but the failure rate of CS is equally high in the american MDs whose school does not use standardized patient model in their clinical education, because you don't how to play the game in the test. Nowaday, the failure rate in CMGs (chinese medical graduate) significantly dropped as more and more CS training courses are available, you can spend $300-$600 for a 2-day course, and understand how to encounter with these patients (actors, they evaluate/score you)