The Academy of Motion Picture Arts and Sciences disqualified "Joy" as Austria's entry for best international feature film on the grounds that only 30 per cent of the dialogue is in German and Nigerian languages other than English, said Werner Mueller, the head of the Film And Music Austria (FAMA) industry group.
According to Academy rules, foreign entries have to be predominantly in a non-English language.
Mueller told dpa that the documentary-style "Joy" simply records how these Nigerian women talk to each other in Austria, Mueller said. "They don't talk like on a Vienna theatre stage."
"I am extremely astonished and shocked," director Mortezai told dpa.
She argued that more than half of the dialogue is actually in Nigerian Pidgin English, which is so distinct from standard English that US audiences would not understand it.
Test screenings for non-Nigerian native English speakers showed that large parts of the film needed English subtitles, Mortezai said.
Some linguists view Nigerian Pidgin English as a distinct language from English, while others see a continuum between the two tongues.
"Joy" has received several prizes, including at the Venice Film Festival.
In Nigeria, "Lionheart" director Genevieve Nnaji has pushed back against the Academy's rejection of her film.
"This movie represents the way we speak as Nigerians. This includes English which acts as a bridge between the 500+ languages spoken in our country," Nnaji tweeted last week.
Mortezai said that films without major distribution in the US have little chance to compete for an Oscar except in the international category.
However, she cautioned that softening the Academy's language rule and opening up this category to all non-US films might result in many foreign film entries from English-speaking countries like Australia.
"This would put real non-English films at a competitive disadvantage," she said.
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