[Bug]: `localizeLabels` doesn't apply without translations

[alahwa]

Mapbox Navigation SDK version

2.6.0

Steps to reproduce

Implement localization according to the documentation:

navigationMapView.mapView.mapboxMap.onNext(.styleLoaded, handler: { [weak self] _ in
    self?.navigationMapView?.localizeLabels()
})

Expected behavior

Localization should apply according to system language preferences.

Actual behavior

Localization does not properly apply unless the current system language is also configured in Xcode with a stub localization file. This isn't a feasible solution for our use case, as we have a translation pipeline with several supported languages, and introducing a localization file for every language Mapbox supports isn't possible.

Instead, is there an option to enable language support broadly based on the system language preferences? Why does our app need to be localized for a particular language in order for Mapbox to support it?

Is this a one-time issue or a repeatable issue?

repeatable

[1ec5]

Localization should apply according to system language preferences.

Agreed. Specifically, map label localization should respect the Preferred Language Order setting in Settings ‣ General ‣ Language & Region. The issue is that NavigationMapView.localizeLabels() is consulting Locale.nationalizedCurrent, which is based on the locales into which the application is localized:

mapbox-navigation-ios/Sources/MapboxNavigation/NavigationMapView.swift

Lines 1760 to 1761 in c0b7829

	guard let preferredLocale = VectorSource.preferredMapboxStreetsLocale(for: .nationalizedCurrent) else { return }
	mapView.localizeLabels(into: preferredLocale)

mapbox-navigation-ios/Sources/MapboxCoreNavigation/Locale.swift

Lines 4 to 25 in c0b7829

	/**
	Given the app's localized language setting, returns a string representing the user's localization.
	*/
	public static var preferredLocalLanguageCountryCode: String {
	let firstBundleLocale = Bundle.main.preferredLocalizations.first!
	let bundleLocale = firstBundleLocale.components(separatedBy: "-")
	if bundleLocale.count > 1 {
	return firstBundleLocale
	}
	if let countryCode = (Locale.current as NSLocale).object(forKey: .countryCode) as? String {
	return "\(bundleLocale.first!)-\(countryCode)"
	}
	return firstBundleLocale
	}
	/**
	Returns a `Locale` from `preferredLocalLanguageCountryCode`.
	*/
	public static var nationalizedCurrent = Locale(identifier: preferredLocalLanguageCountryCode)

This behavior is appropriate for Locale.nationalizedCurrent, which is designed to ensure consistency between the navigation SDK’s UI “chrome” and the rest of the application’s UI. However, it’s inappropriate for “content” displayed within the application that comes from other sources. In the case of a navigation application, map labels would probably be considered content.

This regression was introduced in #3330. The older implementation in #1111 (itself based on a map SDK implementation) solely relied on Locale.preferredLanguages, which corresponds to the user setting (modulo Mapbox Streets source support):

mapbox-navigation-ios/Sources/MapboxNavigation/VectorSource.swift

Lines 59 to 67 in c0b7829

	if let locale = locale {
	preferences = [locale.identifier]
	} else {
	preferences = Locale.preferredLanguages
	}
	guard let preferredLocalization = VectorSource.preferredMapboxStreetsLocalization(among: preferences) else {
	return nil
	}

It should be straightforward to switch over to Locale.preferredLanguages. I don’t think it would be considered a backwards-incompatible change, as it would fix unexpected behavior in languages unsupported by the application but leave the behavior unchanged in supported languages.

As a temporary workaround, you can call the map SDK’s Style.localizeLabels(into:forLayerIds:) method directly. You can use Locale.preferredLanguages, but note that this method throws an error that you’ll need to catch if the Mapbox Streets source doesn’t support the user’s preferred language. The other caveat is that it localizes everything on the map, not only places and POIs but also road names.

Incidentally, Locale.nationalizedCurrent is also being used by NavigationRouteOptions to request spoken and visual guidance instructions in the same language as the UI:

mapbox-navigation-ios/Sources/MapboxCoreNavigation/NavigationRouteOptions.swift

Line 145 in c0b7829

locale = Locale.nationalizedCurrent

This is a tougher call; whether guidance instructions are considered “chrome” or “content” probably depends on the application’s UI design.