B777-200 FLT CREW MISINTERPED CTLR CLRNC DUE TO LANGUAGE BARRIER AND DSNDED BELOW INTENDED ASSIGNED ALT. A NEW HDG WAS ISSUED TO MAINTAIN SEPARATION WITH ANOTHER ACFT.

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CRUISING AT FL370 AND ON A HDG; WE WERE CLRED TO FL330 BY TOKYO CTL. WE HAD TO RECONFIRM THIS CLRNC SEVERAL TIMES BEFORE ACCEPTING IT DUE TO GREAT DIFFICULTY IN UNDERSTANDING THIS PARTICULAR FEMALE CTLR. DURING THE DSCNT; WE BELIEVE WE WERE GIVEN FURTHER DSCNT TO FL310 AND ALSO ADVISED OF TFC AHEAD AT FL310. AGAIN; WE ASKED THE CTLR TO CONFIRM THE DSCNT TO FL310 AND RECEIVED CONFIRMATION. UPON DSNDING THROUGH APPROX FL320 WE RECEIVED A CLRNC TO MAINTAIN FL330 AND GIVEN AN APPROX 50 DEG TURN TO THE R. WE DID RECEIVE AN AMBER TCASII 'TFC ALERT' AT THE COMMENCEMENT OF THE TURN. NO TCASII RA WAS EVER ANNOUNCED. UPON REACHING THE OFFSET HDG; WE ASKED IF FL320 WAS OK AND GIVEN A ROGER. WE WERE THEN CLRED LOWER AFTER CLR OF TFC AND GIVEN DIRECT THE ORGAN FIX. HUMAN FACTORS: EXTREME DIFFICULTY IN UNDERSTANDING CTLR. HER SPEECH IS WAY TOO FAST AND RUNS HER WORDS TOGETHER. WE BELIEVE THAT SHE WAS ALSO HAVING TROUBLE UNDERSTANDING OUR COMS. IN RETROSPECT; WE THINK SHE WAS ACKNOWLEDGING THAT WE SAW THE TFC AT FL310 AND REPLIED WITH A ROGER TO OUR ASKING FOR CONFIRMATION OF BEING CLRED TO FL310. ANOTHER ISSUE WAS THAT SHE WAS HAVING TO DEAL WITH WAS AN UNUSUALLY HIGH TAILWIND; 156 KTS FOR US AND THE RECIPROCAL HEADWIND WITH THE TFC AT FL310. WE DID ASK THE RJTG OPS AGENT TO COMMUNICATE OUR UNDERSTANDING OF THIS EVENT WITH THE TOKYO ATC SUPVR. SUPPLEMENTAL INFO FROM ACN 637169: WE WERE AT CRUISE ALT WITH A 145 KT TAILWIND ON OUR WAY INTO NARITA AND SHOULD HAVE BEGUN OUR DSCNT. WE HAD REQUESTED LOWER FROM THE CTLR. SHE WAS A LITTLE BEHIND IN ALLOWING ACFT TO DSND DUE TO THE STRONG TAILWIND AND WHEN WE DID RECEIVE ALT CHANGES; THEY WERE VERY MODEST -- ONLY A COUPLE THOUSAND FT AT A TIME RESULTING IN US BEING EXTREMELY HIGH. THE INCIDENT OCCURRED WHEN SHE GAVE US AN ALT CHANGE. BOTH MYSELF AND THE CAPT WERE HAVING GREAT DIFFICULTY UNDERSTANDING HER CLRNC (AND QUESTIONED HER SEVERAL TIMES ABOUT AN ALT CHANGE. WE BOTH HAD OUR EAR PIECES IN OUR EARS).