When I run speechSynthesis.getVoices() in Chrome, I get a list of possible voices. The list changes depending on the computer and version of Chrome.

Is there any way I can extend support and add more voices?

I feel like this could be done by asking a user to download a voice file for their chosen language. Do such files exist?

Edit:

This needs to work for both Windows and Mac computers.

It also needs to be simple, so no scripts or anything that would require extensive technical knowledge. I'm hoping for a "download and install" type of thing

HOW TO ADD MORE VOICE FROM MICROSOFT EDGE TO CHROME AND FIREFOX ( only on windows 10 fall creator update or later)

you should using show list voice test first at: show available voice on browser

chrome have local and server voice, edge have local and can download more, firefox have nothing else but only 3 supported voice locked by windows registy.

Here's the script to unlock:

If your not sure how to run a powershell script:

Click Start

search for 'Powershell'

launch Powershell (Since this is editing a LocalMachine key, you will need to run as admin). Copy and paste the script into the console. Press enter.

$sourcePath = 'HKLM:\software\Microsoft\Speech_OneCore\Voices\Tokens' #Where the OneCore voices live
$destinationPath = 'HKLM:\SOFTWARE\Microsoft\Speech\Voices\Tokens' #For 64-bit apps
$destinationPath2 = 'HKLM:\SOFTWARE\WOW6432Node\Microsoft\SPEECH\Voices\Tokens' #For 32-bit apps
cd $destinationPath
$listVoices = Get-ChildItem $sourcePath
foreach($voice in $listVoices)
{
$source = $voice.PSPath #Get the path of this voices key
copy -Path $source -Destination $destinationPath -Recurse
copy -Path $source -Destination $destinationPath2 -Recurse
}

After running this on my Example machine and restarting, I have the following voices available to the api

Microsoft David Desktop; Microsoft Zira Desktop; Microsoft Zira Mobile; (Same as the desktop counterpart) Microsoft Mark Mobile;

I find these voices to be superior to the Desktop variants, plus variety is always nice

that you can test your new voice here after restart: show available voice on browser

here I can have 10 voices than 3 voices before, on firefox. That even I can install Vietnamese voice with Microsoft An from windows language, and my firefox can read vietnamese as edge.