Composing Text Providers with  CLKTextProvider.​localizableTextProvider(​withStringsFileFormatKey:, textProviders:)

Are there any official examples of setting up a complication using localizableTextProvider(withStringsFileFormatKey:, textProviders:)? I can get the text provider to populate when producing a SampleTemplate, but whenever I try to generate a template using getTimelineEntries the text provider generated by localizableTextProvider the result is always blank, no text.

Example (only supporting .utilitarianLarge):

func getCurrentTimelineEntry(for complication: CLKComplication, withHandler handler: @escaping (CLKComplicationTimelineEntry?) -> Void) {
        // Call the handler with the current timeline entry
        let template = CLKComplicationTemplateUtilitarianLargeFlat()
        
        template.textProvider = CLKTextProvider.localizableTextProvider(
            withStringsFileFormatKey: "testComplication",
            textProviders: [
                CLKSimpleTextProvider(text: "Hello"),
                CLKSimpleTextProvider(text: "World")
            ]
        )
        
        handler(CLKComplicationTimelineEntry(date: Date(), complicationTemplate: template))
        
    }

and sampleTemplate as

func getLocalizableSampleTemplate(for complication: CLKComplication, withHandler handler: @escaping (CLKComplicationTemplate?) -> Void) {
        // This method will be called once per supported complication, and the results will be cached
        switch complication.family {
        case .utilitarianLarge:
            let template = CLKComplicationTemplateUtilitarianLargeFlat()
            
            template.textProvider = CLKTextProvider.localizableTextProvider(
                withStringsFileFormatKey: "testComplication",
                textProviders: [
                    CLKSimpleTextProvider(text: "Hi"),
                    CLKSimpleTextProvider(text: "World")
                ]
            )
            
            handler(template)
            
        default:
            handler(nil)
        }
        
    }

with ckcomplication.strings as

"testComplication" = "%@ %@";

The sample template will always display the text "Hi World", whereas the result from getCurrentTimelineEntry will always display an empty complication.

Has anyone had luck composing text providers in this way?