Android, Locale utilities: get a currently displayed locale at a device's system level, validate a locale or a language tag

CurrentlyDisplayedLocale.kt

/**
 * Licensed under the BSD-3-Clause-Clear license. 
 * The license text in enclosed in the comment section.
 */


/**
 * The idea is to use the hidden SYSTEM_LOCALES ("system_locales") setting 
 * to get the currently displayed locale. Although the documentation says
 * that one must use `LocaleList.getDefault` instead, I couldn't really 
 * get the right locale when I changed it in the system settings.
 */


/**
 * @return currently displayed locale at a device's system level or null
 */
fun getCurrentLocale(context: Context): Locale? {
    val devicesLocales = Settings.System.getString(
        context.contentResolver,
        "system_locales"
    )

    val displayedLocale = if (devicesLocales != null && devicesLocales.isNotEmpty()) {
        // get the first language as it is what is currently displayed for the user
        val locales = devicesLocales.split(",")
        val languageTag = locales[0]

        // retrieve locale from the language tag
        Locale.forLanguageTag(languageTag)
    } else {
        // it should be unreachable, but you never know
        null
    }

    return displayedLocale
}

/**
 * @param fallbackLocale must be set in case the device's locale is not retrievable
 * @return currently displayed locale at a device's system level or `fallbackLocale`
 */
fun getCurrentLocale(context: Context, fallbackLocale: Locale): Locale {
    return getCurrentLocale(context) ?: fallbackLocale
}

LocaleValidator.kt

/**
 * Licensed under the BSD-3-Clause-Clear license. 
 * The license text in enclosed  in the comment section.
 */


fun isLocaleValid(locale: Locale): Boolean {
    val availableLocales = Locale.getAvailableLocales()
    return locale in availableLocales
}

fun isLanguageTagValid(languageTag: String): Boolean {
    val availableLanguageTags = Locale.getAvailableLocales().map { it.toLanguageTag() }
    return languageTag in availableLanguageTags
}

LICENSE

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