src/vs/workbench/api/common/extHostLocalizationService.ts/ExtHostLocalizationService/initializeLocalizedMessages
class ExtHostLocalizationService:	async initializeLocalizedMessages(extension: IExtensionDescription): Promise<void> {
		if (this.isDefaultLanguage
			// TODO: support builtin extensions
			|| (!extension.l10n && !extension.isBuiltin)
		) {
			return;
		}

		if (this.bundleCache.has(extension.identifier.value)) {
			return;
		}

		let contents: { [key: string]: string } | undefined;
		const bundleUri = await this.getBundleLocation(extension);
		if (!bundleUri) {
			this.logService.error(`No bundle location found for extension ${extension.identifier.value}`);
			return;
		}

		try {
			const response = await this._proxy.$fetchBundleContents(bundleUri);
			const result = JSON.parse(response);
			// 'contents.bundle' is a well-known key in the language pack json file that contains the _code_ translations for the extension
			contents = extension.isBuiltin ? result.contents?.bundle : result;
		} catch (e) {
			this.logService.error(`Failed to load translations for ${extension.identifier.value} from ${bundleUri}: ${e.message}`);
			return;
		}

		if (contents) {
			this.bundleCache.set(extension.identifier.value, {
				contents,
				uri: bundleUri
			});
		}
	}