A320 FLT CREW EXPERIENCED TCASII RA WITH FOREIGN ACR ON APCH TO ORD AT 8000 FT UNDER C90 CTL.

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WE WERE AT 8000 FT ON A HEADING OF 040 DEGS; APPROX 10 MI SW OF ORD; BTWN LAYERS; BEING VECTORED TO RWY 9R. THE FO WAS FLYING ON AUTOPLT AT THE TIME. IT WAS EXTREMELY BUSY ON APCH CTL. I HEARD ATC GIVE ACR Y A HEADING. IT TOOK 3 TIMES FOR THE CTLR TO UNDERSTAND WHAT ACR Y WAS READING BACK. DURING THAT EXCHANGE; I HEARD THE CTLR AND ACR Y BOTH SAY '260.' ABOUT 1 MIN LATER; I SAW LNDG LIGHTS COMING STRAIGHT AT US (IT TURNED OUT TO BE ACR Y). I LOOKED AT THE TCASII AND HE WAS AT OUR ALT AND WAS ABOUT 6-7 MI AWAY. I ASKED APCH ABOUT THE ACFT AND HE TOLD US TO TURN TO A 090 DEG HDG. THE FO BEGAN THE TURN. I TOLD THE FO TO BE READY FOR A TCASII. PASSING ABOUT 060 DEGS WE GOT A TCASII RA TO DSND. THE FO DID A GREAT JOB. HE DISCONNECTED THE AUTOPLT AND CONTINUED TURNING WHILE GOING INTO A DSCNT; JUST OUT TO THE 'RED;' OF 1100-1200 FPM. I TOLD ATC WE WERE DSNDING FOR A TCASII. AT NO TIME DID I LOSE SIGHT OF ACR Y. HE PASSED OFF OUR L ABOUT 1-2 MI AND WHEN HE WAS ABEAM US; THE TCASII WAS RESOLVED. WE WERE AT ABOUT 7200 FT. I TOLD ATC WE COULD GO TO ANY ALT NOW AND THEY WANTED US TO CLB BACK TO 8000 FT AND SAID 'TO TURN TO 260.' I RESPONDED WITH 8000 FT AND SAID 'R TO 260' SINCE THAT WAS THE WAY WE WERE TURNING. HE SAID TO TURN L; WHICH WE THEN DID. HE THEN ASKED ACR Y IF HE WAS ON A 360 DEG HDG AND ACR Y SAID HE WAS ON THE 260 DEG ASSIGNED. THERE WAS A SHORT PAUSE AND I RECALL THE CTLR SAYING 'SORRY' TO THE ACR Y. SHORTLY LATER; THERE WAS A NEW VOICE ON ATC. WE LANDED ON RWY 9R WITHOUT ANY FURTHER PROBS. CHANNEL 9 WAS ON AND SEVERAL PAX COMMENTED ON THE TCASII. ONE SEEMED TO KNOW WHAT HAD OCCURRED. I TOLD THEM THAT I HAD THE ACFT IN SIGHT AT ALL TIMES AND IT WASN'T THAT BIG OF A DEAL.