A CARGO TRIJET CAPT RPTED THAT THE RKSI TRACON CTLR WAS HARD TO UNDERSTAND WHICH CAUSED THE CREW TO MISUNDERSTAND THEIR CLRNC.

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WE HAD JUST SLOWED FROM (AN APPROVED) HIGH SPD DSCNT AND WERE UNDER RADAR VECTORS FROM THE FINAL CTLR AT INCHEON INTL; KOREA (RKSI). THERE WAS PRECEDING TFC; AND RADIO COM WAS HVY. THE CTLR WAS DIFFICULT TO UNDERSTAND DUE TO HIS CONSIDERABLE ACCENT. ADDITIONALLY; THERE WAS RADIO TFC ON GUARD (121.5); ADDING TO THE CACOPHONY. WE HAD BEEN ASSIGNED A HDG OF 270 DEGS; AND AT ABOUT 15 MI; ALL 3 OF US THOUGHT WE HEARD 'MAINTAIN 300 DEGS; INTERCEPT THE LOC.' THE CAPT READ BACK THESE INSTRUCTIONS; AND ABOUT 10 SECONDS LATER; WE BEGAN ROLLING OUT ON THE LOC TO RWY 33R. THE CAPT THEN RADIOED 'INTERCEPTING LOC' AT WHICH POINT AN EVIDENTLY ALARMED CTLR REPLIED THAT WE WERE TO 'MAINTAIN 300 DEGS AND FLY THROUGH THE LOC.' WE IMMEDIATELY TURNED BACK TO 300 DEG HDG. AFTER SOME MORE HVY RADIO CHATTER TO OTHER ACFT; THE CTLR INQUIRED AS TO WHY WE INTERCEPTED THE LOC. WE REPLIED THAT THIS WAS WHAT WE UNDERSTOOD HIS INSTRUCTIONS TO BE; AND THAT HIS COMS WERE DIFFICULT TO UNDERSTAND. WE FURTHER THOUGHT; ALTHOUGH WE DID NOT COMMUNICATE THIS; THAT THIS INQUIRY IN THE MIDDLE OF OUR APCH WAS HIGHLY INAPPROPRIATE. AT NO TIME DID WE GET NEAR OTHER TFC -- OUR CLOSEST TFC BEING THE PRECEDING FLT AT 4 MI. AFTER A FEW MORE ATC DIRECTED S-TURNS; WE CAPTURED THE ILS AND FLEW AN UNEVENTFUL APCH TO RWY 33R. WE HEARD NO FURTHER INQUIRIES ON THE GND.