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Adding i18n to your application#

Every single label or message in your application that may be read by an end-user should use the i18n system. You should never type in plain English directly in your HTML or JavaScript files, even if you're currently releasing your app in only one language.

In this document, you will learn how to properly use the i18n system in Monster-UI.

Create the i18n files#

Where to create them?#

First, you need to create your i18n files. If you used the skeleton app as a starter, you should already have an i18n folder with two files in it (en-US.json for American ENglish and fr-FR.jsfor French).

If not, you need to create this i18n folder at the root of your application, and then add a new file in it with the name en-US.json, like so apps/demoapp/i18n/en-US.json

The fr-FR.json file is only provided as an example and may be discarded. The en-US.json file is however mandatory, en-US being the fallback language by default. This means that if the system can't find a specific key in a language file, or can't find the language file itself, it will automatically fallback to en-US.

You can then add a new file for any language you want by using the same naming system xx-YY.json, where xx is the language code (ISO 639-1) and YY is the country code (ISO 3166).

What to put in them?#

This is where you will put your actual labels, messages and others by using a simple key/value mapping in JSON.

The keys will be used in your JavaScript files or HTML templates in order to retrieve the attached values, the values being your actual text.

Thanks to the JSON format, you can also bind an array or an object to a key, instead of a simple string, which will allow you to better organize your i18n file.

You can also add variables inside your strings by using two pairs of curly brackets: {{myVariable}}.

Here is an example of what an i18n file would look like for a very basic app:

    "title": "Hello {{variable}}! Welcome to the Demo App.",
    "description": "This is a demo app that does nothing, click on the button below to see a popup",
    "button": "Click here!",
    "popup": {
        "title": "Random Number Generator",
        "content": "We've generated the random number {{number}} for you."

Use the i18n files#

In JavaScript files#

At the top of your app.js file, you should declare the list of languages supported for your app. Again, if you started from the skeleton app, this should already be done.

var app = {
    name: 'demoapp',
    i18n: {
        'en-US': { customCss: false },
        'fr-FR': { customCss: false }
    /* ... */

The language file for your selected language will then automatically be merged into the app during the app initialization. To access it, simply call the function, this will return you the i18n file as a JSON object. The selected language is a setting on the account or user. If the user isn't logged in, it will take the browser language of what's defined in the config.js if set.

If you defined a variable, you will need to use the monster.template() function to replace it by the value of your choice.

The first argument for this function should be the app itself, by convention defined in a variable self (see Coding Standards). The second argument should be your i18n string, prepended with a !.

The last argument should be an object containing your variables and their values. Obviously, the keys from this object must match the variables defined in your i18n string.

    /* ... */
    bindEvents: function(template) {
        var self = this;

        template.find('#demoapp_button').on('click', function(e) {
            var randomNumber = Math.floor(Math.random() * 100),
                popupContent = '<p>' + monster.template(self, '!' +, { number: randomNumber }) + '</p>'

            monster.ui.dialog(popupContent, {
    /* ... */
Customize the CSS based on the language#

Sometimes, a text that is really short in English will be super-long in French and it might look better if we tweaked the CSS a little bit for the French i18n. In order to do that, 3 steps:

  1. we need to set the customCss key to true in the i18n map at the beginning of the app
    i18n: {
        'en-US': { customCss: false },
        'fr-FR': { customCss: true }
  2. check if the cssI18n folder exists in apps/%appName%/style and if it doesn't, create it.
  3. Finally, create a fr-FR.css file in this folder, and add your customizations in this file

This way, the changes will only be loaded for the customers using the French version. If you're using the English version, it won't even load the file.

In HTML templates#

When invoking a template with the monster.template() function, you always provide your app as a parameter, which then automatically passes down your i18n object to the template itself. You can then access it as any other parameters sent to the template, through the i18n variable.

If you defined a variable, you need to user the handlebar helper replaceVar to replace it with the value of your choice. Note: for this to work, your variable must be called {{variable}}, and there should not be more than one variable in your string. If you want to use more variables or variables with custom names, you should handle it on the JavaScript side and pass down your fully formated string to the template.

monster.template(self, 'layout', { username: 'Al Cohol' });
<div id="demoapp_container">
    <div class="demoapp-content">
        <h1>{{replaceVar i18n.title username}}</h1>
        <p>{{ i18n.description }}</p>
        <button id="demoapp_button" type="button">{{i18n.button}}</button>

How to change your language#

The language is defined at both the Account and User level. By default, the user uses its Account language, which may only be changed by an account administrator. Each user can however change their own language in their user settings, by clicking on their name on the top-right corner of the page (when logged in Monster-UI), and then clicking on the "Timezone & Language" section under "User Settings".

Timezone and Language settings

If the language is not defined in neither the Account nor the User, the cookie's language will be used.

Determine the language when not user is logged in:

cookie config.js language used
undefined undefined en-US
undefined fr-FR fr-FR
fr-FR undefined fr-FR
fr-FR en-US fr-FR

Determine the language when a user is logged in:

cookie account user language used
en-US undefined undefined en-US
en-US undefined en-GB en-GB
en-US en-GB undefined en-GB
en-US en-GB fr-FR fr-FR