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Translations of Comprehensive Rust 🦀

We would love to have your help with translating the course into other languages! Please see the translations page for the existing translations..

We use the Gettext system for translations. This means that you don't modify the Markdown files directly: instead you modify .po files in a po/ directory. The .po files are small text-based translation databases.

Tip: You should not edit the .po files by hand. Instead use a PO editor, such as Poedit. There are also several online editors available. This will ensure that the file is encoded correctly.

There is a .po file for each language. They are named after the ISO 639 language codes: Danish would go into po/da.po, Korean would go into po/ko.po, etc. The .po files contain all the English text plus the translations. They are initialized from a messages.pot file (a PO template) which contains only the English text.

We will show how to update and manipulate the .po and .pot files using the GNU Gettext utilities below.

Preparation

We use two helpers for the translations:

  • mdbook-xgettext: This program extracts the English text. It is an mdbook renderer.
  • mdbook-gettext: This program translates the book into a target language. It is an mdbook preprocessor.

Install both helpers with:

$ cargo install mdbook-i18n-helpers

Creating and Updating Translations

First, you need to know how to update the .pot and .po files.

As a general rule, you should never touch the auto-generated po/messages.pot file. You should also not edit the msgid entries in a po/xx.po file. If you find mistakes, you need to update the original English text instead. The fixes to the English text will flow into the .po files the next time the translators update them.

Tip: See our style guide for some things to keep in mind when writing the translation.

Generating the PO Template

To extract the original English text and generate a messages.pot file, you run mdbook with a special renderer:

$ MDBOOK_OUTPUT='{"xgettext": {"pot-file": "messages.pot"}}' \
  mdbook build -d po

You will find the generated POT file as po/messages.pot.

Initialize a New Translation

To start a new translation, first generate the po/messages.pot file. Then use msginit to create a xx.po file for the fictional xx language:

$ msginit -i po/messages.pot -l xx -o po/xx.po

You can also simply copy po/messages.pot to po/xx.po. Then update the file header (the first entry with msgid "") to the correct language.

Tip: You can use the cloud-translate tool to quickly machine-translate a new translation. Install it with

cargo install cloud-translate

Untranslated entries will be sent through GCP Cloud Translate. Some of the translations will be wrong after this, so you must inspect them by hand afterwards.

Updating an Existing Translation

As the English text changes, translations gradually become outdated. To update the po/xx.po file with new messages, first extract the English text into a po/messages.pot template file. Then run

$ msgmerge --update po/xx.po po/messages.pot

Unchanged messages will stay intact, deleted messages are marked as old, and updated messages are marked "fuzzy". A fuzzy entry will reuse the previous translation: you should then go over it and update it as necessary before you remove the fuzzy marker.

Note: Your PRs should either be the result of running msgmerge or the result of new translation work on the PO file for your language. Avoid mixing the two since it often creates a very large diff, which is hard or impossible to review.

Using Translations

This will show you how to use the translations to generate localized HTML output.

Note: mdbook will use original untranslated entries for all entries marked as "fuzzy" (visible as "Needs work" in Poedit). This is especially important when using cloud-translate for initial translation as all entries will be marked as "fuzzy".

Building a Translation

To use the po/xx.po file for your output, run the following command:

$ MDBOOK_BOOK__LANGUAGE=xx mdbook build -d book/xx

This will update the book's language to xx, it will make the mdbook-gettext preprocessor become active and tell it to use the po/xx.po file, and finally it will redirect the output to book/xx.

Serving a Translation

Like normal, you can use mdbook serve to view your translation as you work on it. You use the same command as with mdbook build above:

$ MDBOOK_BOOK__LANGUAGE=xx mdbook serve -d book/xx

When you update the po/xx.po file, the translated book will automatically reload.

Reviewing Translations

When a new translation is started, we look for people who can help review it. These reviewers are often Googlers, but they don't have to be. To automatically get an email when new PRs are created for your language, please add yourself to the CODEOWNERS file.

When reviewing a translation, please keep in mind that translations are a labour of love. Someone spends their free time translating the course because they want to bring Rust to users who speak their language.

Nothing is published right away after a PR lands for a new in-progress language. It is therefore safe to merge the PR as long as the translation is reasonable. This is often better than leaving 50+ comments since this can be overwhelming for the contributor. Instead, please work with the contributor to improve things in follow-up PRs.

GitHub Suggestions

When reviewing a translation PR, please use the GitHub suggestion feature. This feature allows you to directly write how you think a line or paragraph should be phrased. Use the left-most button in the toolbar to create a suggestion.

The PR author can apply the changes with a single click afterwards, drastically reducing the number of round-trips needed in a review.

Incomplete Translations

When the first 1-2 days of the course have been translated, we can publish the translation and link it from the translations page. The idea is to celebrate the hard work, even if it is incomplete.