I stay about 10-15 nights a year at str bkk.
I believe the service has improved over the past few visits. The language barrier imo has improved.
Siam area is less than 10 min walk
I stayed at this St. Regis myself back in November, and believe that the service was quite good (I transferred to the Royal Orchid Sheraton afterwards, which although has good service, is not a St. Regis), and I never once had an issue with English as a language barrier. As kkl identified as well, you can easily walk to CentralWorld within a few minutes, and the hotel is actually right adjacent to a transit station.
For transfers, it's also a flat-rate 1000 THB (plus 75 THB in tolls) to/from the airport in an Uber.