(a) China
(i) Putonghua or "Mandarin" Chinese (or, usually, just "Chinese")
(ii) ditto

(b) Malaysia
(i) Bahasa Melayu (or Bahasa-Malayu)
(ii) ditto

(c) Thailand
(i) Thai
(ii) ditto

(d) India
(i) Hindi
(ii) Since Independence/the Constitution, Hindi - the standard khariboli dialect in the Devanagiri script. But English remains an alternate official _working_ language.