The English version of Samsung's voice assistant Bixby may not be available in the US at least until late June.

Samsung earlier said the key features of Bixby such as Vision, Home and Reminder would be available, but its voice function that allows users to command the phone to perform tasks would be available later this spring.

People with knowledge of the matter told the Wall Street Journal that the English-language version of Bixby is still weeks away from being completed. While there is no word on the release date, recent internal tests suggest Bixby is struggling to understand English syntax and grammar.

A Samsung spokesperson told the WSJ, "Bixby Voice benefits from time to further enhance natural language understanding, and we are currently growing our user testing in the U.S. to prepare for launch."

Other features like image-recognition were already available, the spokesperson said.

The voice assistant is one of the selling points for the Galaxy S8 that Samsung is betting on to bring back consumers' trust after it discontinued the fire-prone phone Galaxy Note 7.

Experts say it is unclear whether Bixby's delayed launch would affect the sales of Galaxy S8.

Virtual assistants are not a great hit among smartphone users. Market research firm Ovum, after conducting a survey of 4,000 consumers in the US, UK and Asia, estimates only 9% of the consumers use artificial intelligence services, whereas 50% of consumers say they had no interest in the feature.

According to Ovum about 3.5 billion active devices including smartphones, TVs and tablets were using native virtual assistants last year. The research firm predicts the figure to reach 7.5 billion by 2021.

In 2021 Google Assistant will capture about 23% of the market, Bixby at 15%, Apple's Siri at 13% and Amazon's Alexa at 4%.

"Digital assistants are important for consumer loyalty in the future because they will eventually be used more," said Ronan de Renesse, practice leader at Ovum.