Unable to unlocalize a layer’s labels

[1ec5]

Style.localizeLabels(into:forLayerIds:) should have a way to explicitly unlocalize a layer’s labels – that is, make it show names in the local language instead of a specific passed-in language. This was supported in Mapbox Maps SDK v6.x but has regressed as of #480.

Rationale

It should be possible to easily undo what Style.localizeLabels(into:forLayerIds:) does when passing in a specific locale.

It should also be possible to ensure that a layer matches the local language, in the event that the original style hard-coded a particular language. For example, the Mapbox Navigation Day/Night v1 styles hard-code English in its road labels, falling back to the local language. This is suboptimal for the Mapbox Navigation SDK, which is marketed around the world, so it would be beneficial to force the local language name instead of English.

Design considerations

In v6.x and the proof-of-concept port in mapbox/mapbox-navigation-ios#2933, -[NSExpression mgl_expressionLocalizedIntoLocale:] supports two special Locale values, both documented:

• nil automatically selects the first language listed in the system Preferred Content Languages list (+[NSLocale preferredLanguages]) that is also supported by the Streets source.
• A Locale with the identifier mul (the standard ISO 639-2 code for multilingual text) selects the name field, which is typically in the local language.

Unfortunately, neither of these options are available in v10. The locale argument is non-optional, though it isn’t a big deal to pass in the first value in NSLocale.preferredLanguages manually. More problematic is that passing in mul currently crashes, because it isn’t one of the hard-coded locale codes supported by Streets:

mapbox-maps-ios/Sources/MapboxMaps/Style/Style+Localization.swift

Lines 10 to 12 in 34ea7ad

	guard let localeValue = getLocaleValue(locale: locale) else {
	fatalError("This locale is not supported")
	}

/cc @mapbox/maps-ios @mapbox/navigation-ios

[1ec5]

nil automatically selects the first language listed in the system Preferred Content Languages list (+[NSLocale preferredLanguages]) that is also supported by the Streets source.

mapbox/mapbox-navigation-ios#3330 implements this option with more robust locale selection code ported from map SDK v6.x. However, it isn’t possible for the navigation SDK to implement mul because the map SDK is still responsible for token replacement in the text-field expressions.

[ohjonah]

The locale argument is non-optional, though it isn’t a big deal to pass in the first value in NSLocale.preferredLanguages manually.

@1ec5 - just to confirm, if an unsupported language is passed in, since an exception is returned, on exception, they should be setting a supported language? Or when this function is called, is there a default locale behavior?

[1ec5]

As of #752, if the system is set to an unsupported locale like Bengali and you pass Locale.current into Style.localizeLabels(into:forLayerIds:), the method will throw an error. You could try to pass in each of the remaining locales in Locale.preferredLanguages until one of them doesn’t throw. But if all of the locales are unsupported, for example because the Bengali speaker didn’t set any fallback languages, then the map is left with whatever language was hard-coded in the style, which would be English in the case of Mapbox’s core styles. This issue requests a way to change the labels from that hard-coded language to the local language, which is stored in the name field in the map tiles.

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.