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Working with LinguiJS CLI

@lingui/cli provides the lingui command for extracting, merging and compiling message catalogs. Follow setup instructions to install required packages.

Extracting messages​

We're going to use an app we built in a React tutorial. The extract command looks for messages in the source files and extracts them:

> npm run extract

Extracting messages from source files…
Collecting all messages…
Writing message catalogs…
Messages extracted!

Catalog statistics:
┌──────────┬─────────────┬─────────┐
│ Language │ Total count │ Missing │
├──────────┼─────────────┼─────────┤
│ cs       │     40      │   40    │
│ en       │     40      │   40    │
└──────────┴─────────────┴─────────┘

(use "yarn extract" to update catalogs with new messages)
(use "yarn compile" to compile catalogs for production)

The message catalog will look like this:

{
  "Message Inbox": "",
  "See all <0>unread messages</0> or <1>mark them</1> as read.": "",
  "{messagesCount, plural, one {There's {messagesCount} message in your inbox.} other {There are {messagesCount} messages in your inbox.}}": "",
  "Last login on {lastLogin,date}.": "",
}

It's in a JSON dictionary, where 'key' is message ID and value is an object with some relevant information: translation, defaults and origin for the message.

This catalog is ready for translation. Let's translate it into Czech by filling the translation fields:

{
  "Message Inbox": "Přijaté zprávy",
  "See all <0>unread messages</0> or <1>mark them</1> as read.": "Zobrazit všechny <0>nepřečtené zprávy</0> nebo je <1>označit</1> jako přečtené.",
  "{messagesCount, plural, one {There's {messagesCount} message in your inbox.} other {There are {messagesCount} messages in your inbox.}}": "{messagesCount, plural, one {V příchozí poště je {messagesCount} zpráva.} few {V příchozí poště jsou {messagesCount} zprávy. } other {V příchozí poště je {messagesCount} zpráv.}}",
  "Last login on {lastLogin,date}.": "Poslední přihlášení {lastLogin,date}",
}

If we run the extract command again, we can see in the stats that all messages are translated:

> npm run extract

Catalog statistics:
┌──────────┬─────────────┬─────────┐
│ Language │ Total count │ Missing │
├──────────┼─────────────┼─────────┤
│ cs       │      4      │    0    │
│ en       │      4      │    4    │
└──────────┴─────────────┴─────────┘

Messages extracted!

(use "yarn extract" to update catalogs with new messages)
(use "yarn compile" to compile catalogs for production)

extract merges all translations with new messages, so you can run this command any time without worrying about losing any translations.

tip

Visit the Message Extraction guide to read more about how it works.

Preparing catalogs for production​

Once we have all catalogs ready and translated, we can compile the JSON into a minified JS file with the compile command. This command parses the messages in MessageFormat and compiles them into simple functions. It also adds plural rules to a production ready catalog:

> npm run compile

Compiling message catalogs…
Done!

The locale directory now contains the source catalogs (messages.json) and the compiled ones (messages.js).

Messages added to compiled file are collected in specific order:

  1. Translated message from specified locale
  2. Translated message from fallback locale for specified locale
  3. Translated message from default fallback locale
  4. Message key

It is also possible to merge the translated catalogs into a single file per locale by specifying catalogsMergePath. For example if catalogsMergePath is assigned locales/{locale} then catalogs will be compiled to /locales/cs.js and /locales/en.js.

Cleaning up obsolete messages​

By default, the extract command merges messages extracted from source files with the existing message catalogs. This is safe as we won't accidentally lose translated messages.

However, sooner or later some messages will be removed from the source. We can use the --clean option to clean up our message catalogs:

npm run extract --clean

Validation of message catalogs​

It might be useful to check if all messages were translated (e.g: in a continuous integration runner). The compile command has a --strict option, which does exactly that.

The example output might look like this:

> npm run compile --strict

Compiling message catalogs…
Error: Failed to compile catalog for locale en!
Missing 42 translation(s)

Configuring source locale​

We see that checking for missing translations has one drawback -- English message catalog doesn't require any translations because we're using English in our source code!

Let's fix it by setting sourceLocale in package.json:

package.json
{
    "lingui": {
      "sourceLocale": "en"
    }
}

Running extract again shows the correct statistics:

> npm run extract

Catalog statistics:
┌─────────────┬─────────────┬─────────┐
│ Language    │ Total count │ Missing │
├─────────────┼─────────────┼─────────┤
│ cs          │      4      │    0    │
│ en (source) │      4      │    -    │
└─────────────┴─────────────┴─────────┘

And compilation in strict mode no longer throws an error:

> npm run compile --strict

Compiling message catalogs…
Done!

If you use natural language for message IDs (that's the default), set sourceLocale. You shouldn't use this config if you're using custom IDs (e.g: Component.title).

Catalogs in VCS and CI​

The locale/_build folder and locale/*/*.js (compiled catalogs) are safe to be ignored by your VCS. What you do need to keep in VCS are the json files (locale/*/*.json) that contain the messages for translators. The JavaScript functions that return the actual translations when your app runs in production are created from those json files. See Excluding build files guide for more info.

If you're using a CI, it is a good idea to add the yarn extract and yarn compile commands to your build process.

Further reading​