api.SpeechSynthesisUtterance.lang - Compatibility issue with Opera

[DeepSideEffect]

What type of issue is this?

Browser bug (a bug with a feature that may impact site compatibility)

What information was incorrect, unhelpful, or incomplete?

The information about the incompatibility of the .lang property of SpeechSynthesisUtterance with Opera is correct.
For example, Opera does not respect the language setting, leading to incorrect pronunciation of English text based on the system's default language accent.

This issue disrupts the user experience, as it affects the clarity and accuracy of speech synthesis. This issue is not present in Chrome, Edge, and Firefox.

What browsers does this problem apply to, if applicable?

Chromium (Chrome, Edge 79+, Opera, Samsung Internet)

What did you expect to see?

I expected the .lang property of SpeechSynthesisUtterance to be fully compatible with Opera, similar to its compatibility with Chrome, Edge, and Firefox.

Specifically, I expected Opera to respect the language setting when specified, and correctly pronounce English text based on the specified language, without defaulting to the system's default language accent.

This would ensure a consistent and accurate speech synthesis experience across all major browsers.

Did you test this? If so, how?

I tested this issue on multiple browsers to compare the behavior of the .lang property of SpeechSynthesisUtterance. Here are the steps I followed:

• Chrome: I set the .lang property to en-GB and tested the pronunciation of an English sentence. The pronunciation was correct, with a British English accent.

• Edge: I repeated the same test as in Chrome, and the pronunciation was also correct, with a British English accent.

• Opera: I set the .lang property to en-GB and tested the pronunciation. However, the pronunciation was incorrect, with a French accent, which is the default language setting of my system.

These tests confirmed that the issue is specific to Opera, as the .lang property is not respected, leading to incorrect pronunciation based on the system's default language accent.

Can you link to any release notes, bugs, pull requests, or MDN pages related to this?

MDN Web Docs - SpeechSynthesisUtterance: lang property: Browser compatibility

Do you have anything more you want to share?

You can test this issue directly and compare with any browser by clicking on the british flag (illustrated below) in the top left corner of the following page

MDN URL

https://developer.mozilla.org/en-US/docs/Web/API/SpeechSynthesisUtterance/lang

MDN metadata

MDN page report details

• Query: api.SpeechSynthesisUtterance.lang
• Report started: 2025-01-10T09:50:44.395Z

[DeepSideEffect]

For more context and to see how this issue affects our project, see this related issue on our GitHub repository.

And I misunderstood the Browser compatibility section of the MDN documentation page at first.
It says not compatible for Opera Android, but should be compatible on Opera since v21 (Released 2014-05-06) --> Full support.