Why does Read Aloud from Immersive Reader sounds different on Android using language "nl" and "nl-BE" but not on iOS while using JavaScript SDK

Question

I have an issue with Immersive Reader which works 100% fine on Android using JavaScript SDK. Read Aloud option sounds different setting the languages: "nl" and "nl-BE" but only on Android. Setting the same values on iOS the Read Aloud speaks the same for both languages.

When sending "options" parameter to the JavaScript function

ImmersiveReader.launchAsync(message.cogSvcsAccessToken, message.cogSvcsSubdomain, data, options);

the "options" has the value for

sampleOptions.disableLanguageDetection = true 

I am setting the "nl" or "nl-BE" here:

sampleChunk = Chunk(content: availableText, lang: "nl-BE", mimeType: "text/html")

Both on iOS and on Android when setting different languages is ok for languages: "ro", "nl", "de" for all these languages Read Aloud sounds different but not on "nl" and "nl-BE" on iOS. Only on Android works well this last option.

Can you clarify me about this please ?