DURING A DUAL FLT OVER HIGH MOUNTAINOUS TERRAIN, THE CFI & HIS STUDENT OBSERVED THE ACTIVATION OF THE TAIL ROTOR CHIP WARNING LIGHT. THE CFI ELECTED TO MAKE A PRECAUTIONARY LDG, & HE ATTEMPTED TO CONVEY THE NEED TO PERSONALLY HANDLE THE ACFT. SEVERAL TIMES THE CFI TOLD HIS STUDENT THAT HE WAS GOING TO MAINTAIN CONTROL, BUT THE FOREIGN STUDENT'S ENGLISH WAS INSUFFICIENT TO ADEQUATELY COMMUNICATE WITH THE CFI, & THE FOREIGN STUDENT DID NOT COMPLY WITH THE CFI'S VERBAL INSTRUCTIONS. DURING THE APPROACH TO THE CLEARING THE STUDENT BECAME NERVOUS, TENSE, & TIGHTLY HELD ON TO THE CONTROLS. THE STUDENT SUBSEQUENTLY RECOGNIZED THAT HIS ACTION INHIBITED THE CFI FROM PROPERLY HANDLING THE ACFT. WHEN A LOW ROTOR RPM CONDITION OCCURRED THE CFI WAS UNABLE TO RECOVER. THE ACFT TOUCHED DOWN HARD & ROLLED OVER. TWO DAYS BEFORE THE ACCIDENT THE OWNER OF THE FLT SCHOOL, WHO WAS A DESIGNEE, ISSUED THE FOREIGN STUDENT AN UNRESTRICTED PLT CERTIFICATE.