When developing applications, no matter it is web / desktop / mobile app. We have to deal with internationalization (i18n) at some point. One interesting finding I had recently was about how iOS devices detect UI culture, especially for Cantonese (Hong Kong).

For developers that comes from Hong Kong should be no stranger to the zh-HK locale code. I assume most developers would expect the same when the device region is set to Hong Kong, the UI culture would be detected as zh-HK.

During development of an app with MAUI, I created AppResources.resx for default (English), AppResources.zh-HK.resx for Traditional Chinese (Hong Kong). But the UI didn’t respect the language settings on my iPhone set to Traditional Chinese (Hong Kong). When I logged the detected UI culture, it showed as yue-Hant-HK.

It turns out that yue is the ISO 639-3 code for spoken Cantonese language, while Hant indicates Traditional Chinese characters. yue-Hant-HK is a valid IETF language tag.

This shows Apple recognizes Cantonese as a separate language, which is appreciated. On Android devices, the detected locale would be zh-HK as expected, which groups the spoken and written forms together. In order to have a single resource file for both platforms, I used the code below:

#if IOS
var ui = CultureInfo.CurrentUICulture;

// Treat any Cantonese tag as zh-HK
if (ui.Name.StartsWith("yue", StringComparison.OrdinalIgnoreCase))
{
    var mapped = new CultureInfo("zh-HK");
    CultureInfo.DefaultThreadCurrentUICulture = mapped;
    CultureInfo.DefaultThreadCurrentCulture = mapped;
}
#endif