FLC OF CPR ADVTECH MLG EXPERIENCES LANGUAGE BARRIER DIFFICULTIES ON OVER-WATER FLT.

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ACFT WAS IN CRUISE FROM RJAA TO PANC AT FL410. COMS UP TO THIS POINT WERE CONDUCTED ON VHF. WITH THE HDOF FROM VHF COMS TO OUR ASSIGNED HF FREQ; THE NEW CTLR REQUESTED WE CLB TO FL430. (THIS WAS AN EARLIER REQUEST BY THE PREVIOUS CTLR ON VHF BUT ADVISED HIM WE DID NOT WANT TO CLB TO FL430 DUE TO WARMER THAN FORECAST ISA TEMP THUS WE WERE CLRED TO CRUISE AT FL410 WITH A FURTHER CLB TO FL430 AT A FIX 725 NM AHEAD; THIS WAS ACCEPTABLE). WE ALSO ADVISED THE NEW CTLR OF THE WARMER THAN FORECAST ISA TEMP AND OFFERED TO DSND (AS LOW AS FL310). INSTEAD WE WERE ISSUED A CLRNC TO CROSS PAWES AT FL420 OR ABOVE; CLRED TO FL430. THE CLB WAS INITIATED MEETING THE XING RESTRICTION AND LEVELED AT FL430. DURING CRUISE WE NOTICED THE SAT FLUCTUATING; AND PROGRESSIVELY INCREASING (ISA +15C). ASSOCIATED ALONG WITH THIS WAS SOME LIGHT TURB. CONTINUED FLT AT THIS ALT WOULD NOT BE PRACTICAL AND REQUESTED A DSCNT TO FL410. CTL SAID THEY WERE UNABLE; WE REQUESTED WE NEEDED THE DSCNT AND WANTED TO BEGIN OUR DSCNT TO FL410 NOW. WE RECEIVED THE CLRNC TO FL410. I FEEL THAT THERE WAS A MISUNDERSTANDING IN THE COMS BTWN THE VHF CTLR AND THE HF CTLR TO THE FACT THAT OUR CLB TO FL430 WAS NOT TO BE INITIATED FOR ANOTHER 700+ NM. TO FURTHER CONFUSE THE ISSUE; THE CTLR DID NOT SEEM TO BE AWARE OF THE EFFECT ON PERFORMANCE THAT THE INCREASED TEMP HAD; AND A DSCNT WAS NEEDED TO OPERATE THE ACFT SAFELY. A CLB TO THE HIGHER ALT LATER COULD BE DONE DUE TO THE REDUCED WT FROM FUEL BURN. ALSO; HF COMS ARE DIFFICULT DUE TO POOR RECEPTION; HVY ACCENTS AND SOMETIMES LESS THAN PERFECT ENGLISH.