B777 FLT CREW FAILS TO COMPREHEND VIDP ALTIMETER SETTING IS IN MB AND NOT INCHES OF MERCURY CAUSING ALT DEV.

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HAD RECENTLY MADE POS CHANGES FOR APCH AND LNDG TO DEL. ONCE EVERYONE ASSUMED THEIR PROPER POS; I EXCUSED MYSELF FROM THE COCKPIT FOR PHYSIOLOGICAL REASONS. WHEN I RE-ENTERED THE COCKPIT; WE WERE IN THE DSCNT AND BEING VECTORED TO AN ILS APCH RWY 10. WHEN DSNDING BELOW TRANSITION ALT; ATC GAVE THE CREW AN ALTIMETER SETTING OF 2997 AND ALTIMETERS WERE SET AT 2997 QNH. I DID NOT QUESTION THE SETTING; AS I AM NOT ISSUED APCH PLATES FOR DEL AND HAD NO WAY TO XCHK APPROPRIATE SETTINGS. ATIS WAS NOT FUNCTIONING AND WE WERE ONLY ABLE TO PULL UP TERMINAL FORECAST WHICH HAS NO ALTIMETER SETTINGS ON IT. SO; WE HAD NO BACK-UP REMINDERS THAT THE ALTIMETER SETTING SHOULD HAVE BEEN IN MILLIBARS. ONCE LEVEL AT 2600 FT APPROX 2 MI OUTSIDE OF THE FAF; WE WERE DIRECTED TO CLB IMMEDIATELY AND THAT WE WERE AT THE WRONG ALT. WE QUERIED ATC ABOUT THE ALT AND ALTIMETER SETTING AND TWICE HE SAID THE ALTIMETER WAS 2997 (WHICH WE HAD) AND THE THIRD TIME STATED SET QNH 2997! WE TOLD HIM WE WOULD CLB UP TO AND INTERCEPT THE GS; WHICH HE ACCEPTED. ONCE ON THE GND; WE ADJUSTED OUR ALTIMETERS TO FIELD ELEVATION AND DETERMINED THAT WE SHOULD HAVE HAD 997 MILLIBARS SET! COM WAS POOP BTWN THE CTLR AND US; IN THAT HE WAS VERY DIFFICULT TO UNDERSTAND AND APPARENTLY WASN'T VERSED IN ENGLISH AS HE NEVER CAUGHT THAT WE WERE READING BACK 2997 QNH. WE FIGURED AFTERWARD THAT HE MAY HAVE BEEN STATING SET ALTIMETER 'TO' 997 -- BUT THAT IS A GUESS! CORRECTION GIVE: GIVE THE RELIEF PLTS APCH PLATES! A FEW DOLLARS SAVED ISN'T WORTH LOSING LIVES AFTER FLYING 14.5 HRS ALL NIGHT AND AT A VERY DEGRADED LEVEL OF COMPETENCE. SUPPLEMENTAL INFO FROM ACN 791518: DURING A NORMAL APCH IN CLR SKIES AT NIGHT INTO DEL; WE WERE UNABLE TO GET AN ATIS RPT. WE REQUESTED AN ALTIMETER SETTINGS AS WE WENT THROUGH THE TRANSITION ALT AND HEARD 2997. SINCE DEL USES 'HPA' WE ASKED APCH TO CONFIRM AND ALL 4 OF US HEARD 2997. AT THE SAME TIME WE WERE TURNING TO INTERCEPT FINAL AND CLRED TO DSND TO 2600 FT AND CLRED FOR THE ILS TO RWY 27. AS WE LEVELED; WE ASKED TO CONFIRM ALTIMETER IS 2997 AND APCH CTL SAID HE SHOWED US LOW AND TO CLB TO 2600 FT. I DISENGAGED THE AUTOPLT AND CLBED AND WE ASKED AGAIN IF THE ALTIMETER SETTING WAS 2997. HE SAID 'YES 2997; CLB TO 2600 FT.' IN JUST A FEW MOMENTS; WE INTERCEPTED THE GS AND FLEW A NORMAL APCH AND LNDG. THE ARPT; RWY AND SURROUNDING AREA WAS IN SIGHT AT ALL TIMES. THE CORRECT ALTIMETER SETTING WAS 997 MILLIBARS WHICH IS WHAT APCH WAS PROBABLY SAYING; BUT KEPT REPEATING WHAT WE WERE SAYING AS 2997. THE SIMILARITY OF THE NUMBERS; DISTRS OF THE APCH FOR BOTH PLT AND CTLR; AND THE LANGUAGE BARRIER ALL CONTRIBUTED TO THE ERROR.