src/vs/platform/extensionManagement/common/extensionsScannerService.ts/ExtensionsScanner/findMessageBundles
class ExtensionsScanner:	private findMessageBundles(extensionLocation: URI, nlsConfiguration: NlsConfiguration): Promise<{ localized: URI; original: URI | null }> {
		return new Promise<{ localized: URI; original: URI | null }>((c, e) => {
			const loop = (locale: string): void => {
				let toCheck = joinPath(extensionLocation, `package.nls.${locale}.json`);
				this.fileService.exists(toCheck).then(exists => {
					if (exists) {
						c({ localized: toCheck, original: joinPath(extensionLocation, 'package.nls.json') });
					}
					let index = locale.lastIndexOf('-');
					if (index === -1) {
						c({ localized: joinPath(extensionLocation, 'package.nls.json'), original: null });
					} else {
						locale = locale.substring(0, index);
						loop(locale);
					}
				});
			};
			if (nlsConfiguration.devMode || nlsConfiguration.pseudo || !nlsConfiguration.language) {
				return c({ localized: joinPath(extensionLocation, 'package.nls.json'), original: null });
			}
			loop(nlsConfiguration.language);
		});
	}