TWR LCL CTLR REQUIRED TO CANCEL TKOF CLRNC OF A DH8C WHEN OBSERVING AN ARPT VEHICLE DRIVE ONTO THE RWY. VEHICLE EARLIER ACKNOWLEDGED INSTRUCTION TO REMAIN OFF THE RWY FOR DEPARTING ACFT.

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ATR42 ON ROLLOUT RWY 8 RPTED IGUANA ON/NEAR RWY 8. CHANGED LNDG SEQUENCE TO RWY 10 FOR 3 ACFT ON FINAL APCH. IGUANA WAS RPTED S OF INTXN 'R' AND VISUAL SCANNING SHOWED RWY 8 CLR. B737 (Z) CLRED FOR TKOF; PORT AUTH VEHICLE (Y) OBSERVED PROCEEDING INSIDE INTXN 'R' HOLD SHORT LINE; WHILE ACFT ON TKOF ROLL. GND CTL VERIFIED VEHICLE UNDERSTOOD INSTRUCTIONS TO REMAIN CLR OF RWY 8. ACFT (X) DH8C CLRED FOR TKOF. PORT AUTH VEHICLE OBSERVED TO ENTER RWY 8 AT INTXN 'W.' CANCELED TKOF CLRNC FOR DH8C. THE REAL CAUSE OF THE VEHICLE DEV WAS THE LANGUAGE BARRIER; AND REQUIRING ENGLISH LANGUAGE PROFICIENCY FOR ARPT PERSONNEL MIGHT HELP IN THE FUTURE. SUPPLEMENTAL INFO FROM ACN 429825: VEHICLE WAS INSTRUCTED TO HOLD SHORT (READ BACK CORRECT); THEN PROCEEDED ACROSS HOLD SHORT LINES. WHEN QUESTIONED; DID NOT ANSWER BUT EXITED THE RWY AND RPTED CLR. A DASH 8 WAS CLRED FOR TKOF. VEHICLE OBSERVED ENTERING THE RWY AGAIN; DASH 8 CLRNC CANCELED. UNDERSTANDING OF THE ENGLISH LANGUAGE IS AN ONGOING PROB. THE VEHICLE ASKED TO PROCEED EBOUND THEN DROVE BACK ON THE RWY.