is 1:30 min sufficient to transit at Beijing Capital Airport?

If you don't need to transfer in different terminals, then your time is sufficient if you hurry up. The transfer procedure are as follow:

STEP1:Flight Arrival

STEP2:Transfer Procedures

STEP3:Border Inspection

STEP4:Security Check

STEP5:Custom Inspection

STEP6:Flight Waiting and Boarding

Yes, most of the staff can understand English.

can you please let me know how i will go the airchina will help me in going on the right way after i arrive at the airport.
When i will land on beijing is the bus will come for pickup and did they will say that where should i go for international to international transfer.

Upon landing, there are clear English signs at the airport that can help you find directions.
The transfer area will have some staff that can help you a lot.

In addition, do you mean the free airport terminal buses? If yes, you can wait for the bus at T1: outside Gate 7 F1, T2: outside Gate 7 F1, T3: Gate 5 F1 and the bus route is as follow:Gate 5 F1 of T.3 -> Departure floor of T2 -> Departure floor of T1 -> Gate 7 of Arrival floor of T2 -> Gate 7 Arrival floor of T1 -> Departure floor of T3.

You can tell the staff where you wanna go. They will remind you when you arrive at your terminal building.