diff --git a/src/browser/main.ts b/src/browser/main.ts
index 647a2d2..aacc832 100644
--- a/src/browser/main.ts
+++ b/src/browser/main.ts
@@ -5,25 +5,82 @@
 
 import RAL from '../common/ral';
 
-import { setPseudo, localize, Options, LocalizeInfo } from '../common/common';
-
+import { setPseudo, localize, Options, LocalizeInfo, isString, MessageFormat, isNumber, format, LocalizeFunc } from '../common/common';
 export { MessageFormat, BundleFormat, Options, LocalizeInfo, LocalizeFunc, LoadFunc, KeyInfo } from '../common/common';
 
-export function loadMessageBundle(_file?: string) {
+let nlsData: { [key: string]: string[] };
+try {
+	// Requiring this file will be intercepted by VS Code and will contain actual NLS data.
+	// @ts-ignore
+	nlsData = require('vscode-nls-web-data');
+} catch(e) {
+	console.error('Loading vscode-nls-web-data failed. Are you running this outside of VS Code? If so, you may need to intercept the import call with your bundled NLS data.');
+	nlsData = {};
+}
+
+interface InternalOptions {
+	locale: string | undefined;
+	language: string | undefined;
+	languagePackSupport: boolean;
+	cacheLanguageResolution: boolean;
+	messageFormat: MessageFormat;
+	languagePackId?: string;
+	cacheRoot?: string;
+}
+
+let options: InternalOptions;
+
+export function loadMessageBundle(file?: string) {
+	if (!file) {
+		// No file. We are in dev mode. Return the default
+		// localize function.
+		return localize;
+	}
+	// Remove extension since we load json files.
+	if (file.endsWith('.js') || file.endsWith('.ts')) {
+		file = file.substring(0, file.length - 3);
+	}
+	if (file.startsWith('/')) {
+		file = file.substring(1);
+	}
+	if (nlsData && nlsData[file]) {
+		return createScopedLocalizeFunction(nlsData[file]);
+	}
 	return function (key: string | number | LocalizeInfo, message: string, ...args: any[]): string {
 		if (typeof key === 'number') {
-			throw new Error(`Browser implementation does currently not support externalized strings.`);
+			throw new Error('Externalized strings were not present in the environment.');
 		} else {
 			return localize(key, message, ...args);
 		}
 	};
 }
 
-export function config(options?: Options) {
+// This API doesn't really do anything in practice because the message bundle _has_ to be loaded
+// ahead of time via 'vscode-nls-web-data'.
+export function config(opts?: Options) {
 	setPseudo(options?.locale?.toLowerCase() === 'pseudo');
 	return loadMessageBundle;
 }
 
+function createScopedLocalizeFunction(messages: string[]): LocalizeFunc {
+	return function (key: any, message: string, ...args: any[]): string {
+		if (isNumber(key)) {
+			if (key >= messages.length) {
+				console.error(`Broken localize call found. Index out of bounds. Stacktrace is\n: ${(<any>new Error('')).stack}`);
+				return;
+			}
+			return format(messages[key], args);
+		} else {
+			if (isString(message)) {
+				console.warn(`Message ${message} didn't get externalized correctly.`);
+				return format(message, args);
+			} else {
+				console.error(`Broken localize call found. Stacktrace is\n: ${(<any>new Error('')).stack}`);
+			}
+		}
+	};
+}
+
 RAL.install(Object.freeze<RAL>({
 	loadMessageBundle: loadMessageBundle,
 	config: config
diff --git a/src/browser/tsconfig.json b/src/browser/tsconfig.json
index ce58932..e1cc8de 100644
--- a/src/browser/tsconfig.json
+++ b/src/browser/tsconfig.json
@@ -2,7 +2,7 @@
     "extends": "../../tsconfig.base.json",
     "compilerOptions": {
         "lib": [
-            "es5",
+            "es2015",
             "dom"
         ],
         "outDir": "../../lib/browser"
diff --git a/src/common/common.ts b/src/common/common.ts
index 111df72..912338a 100644
--- a/src/common/common.ts
+++ b/src/common/common.ts
@@ -91,6 +91,16 @@ export function isDefined(value: any): boolean {
 	return typeof value !== 'undefined';
 }
 
+const toString = Object.prototype.toString;
+
+export function isNumber(value: any): value is number {
+	return toString.call(value) === '[object Number]';
+}
+
+export function isString(value: any): value is string {
+	return toString.call(value) === '[object String]';
+}
+
 export let isPseudo = false;
 
 export function setPseudo(pseudo: boolean) {
diff --git a/src/node/main.ts b/src/node/main.ts
index 484409e..8ae0f85 100644
--- a/src/node/main.ts
+++ b/src/node/main.ts
@@ -10,21 +10,11 @@ import RAL from '../common/ral';
 
 import {
 	format, localize, isDefined, setPseudo, isPseudo, MessageFormat, BundleFormat, Options, TranslationConfig, LanguageBundle, LocalizeFunc,
-	NlsBundle, MetaDataFile, MetadataHeader, I18nBundle, SingleFileJsonFormat, LoadFunc
+	NlsBundle, MetaDataFile, MetadataHeader, I18nBundle, SingleFileJsonFormat, LoadFunc, isString, isNumber
 } from '../common/common';
 
 export { MessageFormat, BundleFormat, Options, LocalizeInfo, LocalizeFunc, LoadFunc, KeyInfo } from '../common/common';
 
-const toString = Object.prototype.toString;
-
-function isNumber(value: any): value is number {
-	return toString.call(value) === '[object Number]';
-}
-
-function isString(value: any): value is string {
-	return toString.call(value) === '[object String]';
-}
-
 function isBoolean(value: any): value is boolean {
 	return value === true || value === false;
 }