Ionic text-to-speech mandarin

I have used the following in my app and it reads out the text in Cantonese. I have also tried zh-TW, with the same result. How can I get the plug-in to read out Mandarin? Thanks.

this.tts.speak(
  {text: this.searchTerm,
   locale: 'zh-CN',
   rate: 0.7
  })

Solved. The above code works after installing the corresponding voice data for Chinese(China) on my Samsung J4 phone. Previously, I only had Chinese(Hong Kong). That’s why the code cannot read out Mandarin.