There is a fascinating post on Language Log on bahasa, the word used to refer to languages in Indonesian, Malay, and various other Southeast Asian languages (many of them which are not Austronesian languages). I am proud to recall that we observed the use of pheasar in Siem Reap, and speculated that this was etymologically linked to bahasa.
Interesting here is the difference between what is signified by Boso Jowo and Phiesa Khmae versus Bahasa Indonesia. Jowo (Javanese) and Khmae (Khmer) are do not refer to states or even nations, they refer to peoples. Bahasa Indonesia and Bahasa Malaysia refer explicitly to the political construct of the state (contrast to Bahasa Melayu, or the Malay language) and the imagined construct of the nation that populates that state. It is not hard to see, then, why the national languages of Malaysia and Indonesia were so historically important for the nationalist movements.
It is also interesting, in this sense, to contrast the Tagalog with Bahasa Indonesia and Bahasa Malaysia. There is no “bahasa Tagalog.” Rather, Tagalog was denoted the Wikang Pambansa in the late 1930s; wikang here is a Malay word for language (at least according to the Tagalog wikipedia entry for wika) which (to my knowledge) has disappeared from Malay, while pambansa denotes “the people” (cf. bangsa Indonesia = Indonesian nation/people). Tagalog must not have adopted the term “bahasa” because the archipelago did not comprise one of the “Indianized” states of Southeast Asia. Yet clearly the process of denoting one vernacular as the language that represents the people of the nation-in-the-making runs in parallel.
This leads me to wonder what exactly Phasa Thai signifies. The language of the state of Thailand (Prathet Thai), or the language of the Thai people (understood as anyone who lives in Thailand, with some fiddling on the margins for Malays and Khmers and Sino-Thai), or the language of the Thai people (understood as an ethnic group distinct from other ethnic groups in Thailand, like Isan). Same thing for Myanma bhasa and others from the mainland.