It is worth noting that there is a principled reason that "Bangla" cannot be the English name for Bengali, namely that in English language names are not an independent lexical category. In many languages the names of languages are expressions (derivatives, compounds, or phrases) meaning "the language of such-and-such a country or people"). This may be overt, as in Japanese (e.g. furansu "France", furansugo "French", Doitsu "Germany", Doitsugo "German", Kankoku "Korea", Kankokugo "Korean"), or covert, as in English and French, where language names are zero-derivatives of the adjective meaning "of or pertaining to such-and-such a country or people". It would be an anomaly for English to adopt "Bangla" as the name of the language while retaining "Bengali" as the adjective. That isn't to say that it couldn't happen, but it is quite unnatural in terms of the current grammar of English and would likely happen only as a result of some significant pressure or widespread contact of English speakers with Bengali. (It would also introduce a disparity of a different sort between English and Bengali since the Bengali adjective is not "bangla". In fact, the Bengali adjective meaning "Bengali" is not phonologically possible in English since it contains a velar nasal in onset position.)
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