B737 FLT CREW REPORTS TCAS TA AND SELF INITIATED AVOIDANCE MANEUVER; DURING DESCENT.

Narrative

HANDED OFF TO ZZZ APCH AT 16000 FT; 20 NM N OF ZZZ VOR. THE ZZZ APCH CTLR IS DIFFICULT TO UNDERSTAND; BUT WE CONFIRM WITH EACH OTHER THAT HE CLRED US FOR THE ZZZ ARR. THE CAPT CROSSES THE VOR AT 15000 FT AND WE HAVE 12000 FT IN THE ALT WINDOW TO MEET THE FIRST RESTR ON THE ARR; WHICH IS AT OR ABOVE 12000 FT AT THE ZZZ 150/7. THE CTLR ASKED OUR SPD; WE TOLD HIM 210 KTS AND HE SLOWED US TO 180 KTS. THE CAPT RAISED THE NOSE TO SLOW THE ACFT AND WE ARE LEVEL AT 14000 FT; BUT STILL ON THE VNAV PATH APCHING THE ZZZ 150/7. THE CTLR ASKED US WHY WE WERE NOT AT 12000 FT (WHICH IS INCORRECT BECAUSE THE RESTR IS AT OR ABOVE 12000 FT). JUST THEN THE CAPT SEES ANOTHER ACFT BOTH VISUALLY AND ON HIS TCAS ABOUT 12 NM AWAY AT OUR ALT POINTING DIRECTLY AT US. THE CAPT IS ON 20 NM RANGE ON HIS EFIS CTL PANEL AND I AM ON 10 NM; WHICH IS WHY I DON'T SEE THE OTHER ACFT YET. THE CAPT REMARKS; 'WHAT IS THAT GUY DOING THERE?;' JUST AS WE RECEIVE A TFC ALERT CALL ON THE TCAS. THE CAPT TURNS OFF THE AUTOPLT AND BEGINS A CLBING R AVOIDANCE MANEUVER. THE OTHER ACFT GETS WITHIN 5 NM AND 300 FT OF US DURING OUR TURN. WE CLBED TO APPROX 14500 FT AND TURNED TO HDG OF 360 DEGS DURING OUR MANEUVER. WE WANTED TO ASK THE CTLR WHAT WAS GOING ON BUT HE WAS IN A HEATED DISCUSSION IN SPANISH WITH THE OTHER ACFT AND WE COULD NOT GET A WORD IN. BECAUSE WE COULD NOT TALK TO THE CTLR WE CONTINUED THE PROFILE THAT WE WERE CLRED FOR AND CROSSED THE VOR AT 10000 FT; SWITCHED TO THE TWR AND WERE CLRED FOR THE ILS RWY 36. WE MADE A NORMAL APCH AND LNDG AND DID NOT RECEIVE ANY CALLS FROM GND OR TWR ABOUT THE INCIDENT THAT JUST HAPPENED. SUPPLEMENTAL INFO FROM ACN 759174: CTLR AND OTHER ACFT IN HEATED CONVERSATION AND COULD NOT 'BREAK' IN SO WE CONTACTED TWR INSIDE FAF. APCH/LNDG UNEVENTFUL. I WAS PF.