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Keep your translations in line - with Preact!

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                        keep your translations in line  -  with preact!

preact-i18nline brings I18nline to Preact via the html translate attribute. I18n doesn't get any easier than this.


preact-i18nline lets you do this:

<p translate="yes">
  Hey {}!
  Although I am <Link to="route">linking to something</Link> and
  have some <strong>bold text</strong>, the translators will see
  <strong><em>absolutely no markup</em></strong> and will only have a
  single string to translate :o

Write your components as you normally would, and just put a translate="yes" attribute on any element/component that needs to be localized. Seriously.

And because the default translation is inline, it will be used as a fallback if a translation is missing or hasn't happened yet.

Best of all, you don't need to maintain separate translation files anymore; I18nline will do it for you.

What is this?

This project is a port of react-i18nliner by Jon Jensen to Preact, a 3kB alternative to React.

How does it work?

preact-i18nline preprocesses your JSX, transforming it into something truly localizable. It infers placeholders for expressions and wrappers for elements/components, and separates the localizable string. At runtime, it localizes the string, interpolating the wrappers and placeholders into the correct locations.

Localizable strings are detected both from the text nodes, as well as from translatable attributes within the translate="yes" element.

preact-i18nline enhances I18nline, so that it can extract any of these translate="yes" strings from your codebase (in addition to regular I18n.t calls). Once you get everything translated, just stick it on I18n.translations and everything will Just Work™.

Project setup

To setup a project with preact-i18nline, we mostly follow the i18nline project setup, with some small changes. The overview of the setup is repeated below, but for most steps please refer to the i18nline project setup docs.

  • Install i18nline and preact-i18nline (see next section)
  • Create a script in package.json to run the command-line tool (see i18nline docs)
  • Add the preact-i18nline/webpack-loader to your Webpack configuration
  • Import I18n and use translate="yes" to render internationalized text.
  • Create an empty file in the out folder (by default: 'src/i18n') named '[locale].json' for each locale you want to support. (see i18nline docs)
  • Run i18nline synch to synch the translation files and index file. (see i18nline docs)
  • import the index file into your project. (see i18nline docs)
  • Call I18n.changeLocale to set the locale (which loads the right translation file on demand, see i18nline docs)
  • Call I18n.on to react to the 'change' event (e.g. by re-rendering) (see i18nline docs)
  • Get your translators to translate all the messages :)


npm install -S i18nline preact-i18nline

Add the Webpack loader

Add this loader to your config, e.g.


  module: {
    loaders: [
      { test: /\.js$/, loader: "preact-i18nline/webpack-loader" }

For Preact CLI

If your app is generated with Preact CLI, Webpack is configured and managed for you. So instead of configuring Webpack directly, we configure Preact CLI:


export default (config, env, helpers) => {
	// Use Preact CLI's helpers object to get the babel-loader
	let babel = helpers.getLoadersByName(config, 'babel-loader')[0].rule;
	// Update the loader config to include preact-i18nline
	babel.loader = [
		{ // create an entry for the old loader
			loader: babel.loader,
			options: babel.options
		{ // add the preact-i18nline webpack loader
			loader: 'preact-i18nline/webpack-loader'
	// remove the old loader options
	delete babel.options;


In the Javascript files you want to translate, import I18n:

import I18n from 'i18nline';

Then, write your JSX and add translate="yes" to any elements you want to translate:


import { h } from 'preact';
import I18n from 'i18nline';

const User = props => (

const Greeting = props => (
  <p class="greeting" translate="yes">
    Hello, <User name="Bob" />!

export default Greeting;

Now you are ready to generate the translation files. Run the i18nline synch command via the script you setup in package.json:

$ npm run i18n

This will generate 3 files for you (in src/18n by default):

  • default.json: the default translations extracted from the source
  • en.json: the translation file for the default locale ('en' by default)
  • index.js: the index file to import into your project

To add additional languages, just add empty files named [locale].json (e.g. 'fr.json', 'de.json', etc) in the same folder and run i18nline synch again. i18nline will populate the empty files with the default translations.

To learn how to change locales and listen to locale change events, refer to the i18nline documentation.



A placeholder will be created for the input:

<label translate="yes">
  Create <input /> new accounts

As well as for arbitrary JSX expressions:

<div translate="yes">
  Welcome back, {}.

By default, placeholder keys will be inferred from the content, so a translator would see "Create %{input} keys" and "Welcome back, %{user_name}". For complicated expressions, these placeholder keys can get a bit long/gnarly. Having to retranslate strings that "changed" just because you refactored some code is terrible, so you can use keys to be a bit more explicit:

<label translate="yes">
  Create <input key="numAccounts" onChange={this.addAccounts} /> new

In this case the extracted string would just be "Create %{num_accounts} new accounts"


Translators won't see any components or markup; they will be replaced with a simple wrapper notation. In this example, the extracted string would be "That is *not* the right answer":

<div translate="yes">
  That is <b>not</b> the right answer


In addition to the "Edit your settings *here*" string, the "Your Account" will also be preprocessed, since it is a valid translatable attribute within a translated element.

<div translate="yes">
  Edit your settings <a href="/foo" title="Your Account">here</a>


From version 2 onwards, i18nline and preact-i18nline should be effectively zero configuration for most projects. Stuff should Just Work.

If you find you need to change the configuration, you can configure i18nline through package.json, i18nline.rc or command line arguments.

If multiple sources of configuration are present, they will be applied in this order, with the last option specified overwriting the previous settings:

  • Defaults
  • package.json
  • .i18nrc file
  • CLI arguments

Refer to the i18nline configuration docs for details.

Auto-config of plugins

Since version 2, i18nline supports auto-config of plugins by looking at the dependencies for your project. So it will automatically detect preact-i18nline for you. You don't have to do anything for it. But just for completeness, here is how you would configure the preact-18nline plugin if you wanted to do it explicitly:


  "i18n": {
    "plugins": [

Extra configuration options

In addition to the i18nline configuration, preact-i18nline adds some options specific to JSX processing:


An array of strings, or a string with (a comma separated list of) tag names that should be translated automatically. Defaults to [].



  "i18n": {
    "autoTranslateTags": ["h1", "h2", "h3", "h4", "h5", "h6", "p"]

These tags will have an implicit translate="yes", keeping your markup simple.

Note that this works for both regular HTML elements, as well as for your own custom components. For example, if you decided you wanted to use a <T> component everywhere instead of translate="yes", you could add it to autoTranslateTags, and its runtime implementation could be as simple as:

const T = (props) => (
  <span {...this.props} />


An array of strings, or a string with (a comma separated list of) tag names that should not be translated automatically. Defaults to [].

Similarly to autoTranslateTags, if you have certain tags you don't want to translate automatically, (e.g. <code>), you can specify those in a similar manner.



  "i18n": {
    "neverTranslateTags": ["code"],

If those are ever nested in a larger translatable element, they will be assumed to be untranslatable, and a placeholder will be created for them.

Tool support

preact-i18nline mainly focuses on Webpack for it's tool support. There is some support for Browserify (untested) or you can roll your own integration.


There is some support for Browserify through this transform, e.g.

$ browserify -t preact-i18nline/browserify-transform app.js > bundle.js

However, to be honest it was inherited from react-i18nliner and I'm not using it myself and haven't tested it in ages so your mileage may vary. If you do use it, please report any issues you may find (and be prepared to make a PR for it).

Roll your own

It's not too hard to roll your own tool support; as you can see in the loader and transform above, the heavy lifting is done by preprocess. So whether you use ember-cli, sprockets, grunt concat, etc., it's relatively painless to add a little glue code that runs preprocess on each source file.

Add the preact-i18nline runtime extensions to i18n

Both i18nline and preact-i18nline add some extensions to i18n.js to help with the runtime processing of the translations.

When you follow the recommended project setup you should not have to worry about this. i18nline will automatically detect preact-i18nline and modify the generated index file to import I18n from preact-inline/i18n instead of from i18nline. That will automatically take care of things. However if you want more control or are not using the generated index file, you can require I18n via preact-i18nline to get a I18n object that has all extensions applied already:

var I18n = require("preact-i18nline/i18n");

You only need to do this in one place (e.g. in your app's main file), because the returned instance is actually the same object as is returned by i18nline. preact-i18nline just adds its extensions to it.

Alternatively, you can apply the extensions manually:

var I18n = // get it from somewhere, script tag, whatever
// if you did not get it from `i18nline`, you need to apply 
// the i18nline extensions manually as well
// finally apply the preact-i18nline extensions

Working with translations

Since preact-i18nline is just an i18nline plugin, you can use the i18nline CLI to extract translations from your codebase; it will pick up normal I18n.t usage, as well as your new translate="yes" components. The easiest way to do this is to add a "scripts" section to your package.json and call i18nline from there:


  "scripts": {
    "i18n": "i18nline synch"

Then you can simply invoke it via NPM as usual:

$ npm run i18n

Refer to the i18nline project setup docs for more information.


What about pluralization? Or gender?

i18nline does support basic pluralization (via i18n-js), but you need to use pure js for that, e.g.

  {I18n.t({one: "You have 1 item", other: "You have %{count} items"}, {count: theCount})}

Every JSX expression makes a placeholder

This kind of gets to a general rule of i18n: don't concatenate strings. For example,

return (
  <b translate="yes">
    You are {this.props.isAuthorized ? "authorized" : "NOT authorized"}

The extracted string will be "You are %{opaque_placeholder}" and the translators won't get a chance to translate the two inner strings (much less without context). So don't do that; whenever you have logically different sentences/phrases, internationalize them separately, e.g.

return (this.props.isAuthorized ?
         <b translate="yes">You are authorized</b> :
         <b translate="yes">You are NOT authorized</b>);

NOTE: A subsequent release of preact-i18nline may add a check for this situation that will cause an i18nline:check failure. You've been warned :)

Cloning this project under Windows

This project's eslint settings force a check on the use of linefeed characters that will fail when the project is cloned with the git core.autocrlf setting set to true, which is the default on Windows. So make sure to change that setting beforehand. The easiest way to do this is probably to git init a new repo for this project and change the setting, and only then add this repo as a remote and pull from it.

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Copyright (c) 2016 by Stijn de Witt and Jon Jensen, released under the MIT license


Keep your translations in line - with Preact!







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