FOREIGN LANGUAGE PROB ACR X CLB TO WRONG ALT.

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ACR X FROM GUA TO DFW. OUR DEP CLRNC WAS TO CLB TO FL390. JUST PRIOR TO TKOF TWR ALSO TOLD US TO CLB TO FL390. AFTER TKOF WE RPTED TO DEP CTL WE WERE CLBING TO FL390. THEY SAID 'ROGER; RPT OUT OF 11000 FT.' WE DID. THE NEXT XMISSION FROM DEP CTL IS WHERE THE PROB STARTS. THE CAPT AND I BOTH UNDERSTOOD THE CTLR TO SAY -- 'X; RPT OUT OF 17000 FT; AND CLB TO FL390.' THIS IS HOW I READ IT BACK WITH NO ADDITIONAL RESPONSE FROM DEP CTL. AT 17000 FT I WAS ATTEMPTING TO MAKE THE RPT; BUT DUE TO RADIO TFC I MADE THE CALL AT APPROX 17700 FT; AND I ANNOUNCED THE CALL AS 'X CLBING OUT OF 18000 FT;' SINCE WE WERE APCHING 18000 FT.' DEP CTL SAID 'X YOU WERE TOLD TO MAINTAIN 17000 FT.' I HAVE NOT BEEN AN ADVOCATE OF TCASII UNTIL THAT DAY -- BUT IT REALLY WORKED FOR US. THE CAPT HAD ALREADY SPOTTED THE TFC AHEAD OF US AND BEGAN TO LEVEL. HE IMMEDIATELY DSNDED BACK TO 17000 FT. DEP SAID OUR TFC HAD BEEN CLRED TO 18000 FT. AT OUR HIGHEST POINT -- APPROX 17000 FT OUR TFC WAS STILL APPROX 1200-1500 FT ABOVE US AND 5-7 MI AHEAD.