src/vs/workbench/services/extensions/node/extensionPoints.ts/ExtensionManifestNLSReplacer/findMessageBundles
class ExtensionManifestNLSReplacer:	private static findMessageBundles(nlsConfig: NlsConfiguration, basename: string): Promise<{ localized: string; original: string | null; }> {
		return new Promise<{ localized: string; original: string | null; }>((c, e) => {
			function loop(basename: string, locale: string): void {
				let toCheck = `${basename}.nls.${locale}.json`;
				pfs.SymlinkSupport.existsFile(toCheck).then(exists => {
					if (exists) {
						c({ localized: toCheck, original: `${basename}.nls.json` });
					}
					let index = locale.lastIndexOf('-');
					if (index === -1) {
						c({ localized: `${basename}.nls.json`, original: null });
					} else {
						locale = locale.substring(0, index);
						loop(basename, locale);
					}
				});
			}

			if (nlsConfig.devMode || nlsConfig.pseudo || !nlsConfig.locale) {
				return c({ localized: basename + '.nls.json', original: null });
			}
			loop(basename, nlsConfig.locale);
		});
	}