# 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..

[translations page]: https://google.github.io/comprehensive-rust/running-the-course/translations.html

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](https://poedit.net/). There are also several online editors
> available. This will ensure that the file is encoded correctly.

> **Important:** You need to run `dprint fmt` after editing the PO file. This
> ensures consistent formatting of the file. You need to install the Gettext
> tools for this, see the Preparation section below.

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.

[Gettext]: https://www.gnu.org/software/gettext/manual/html_node/index.html
[ISO 639]: https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes

## Preparation

### Gettext

You will need the [Gettext] utilities (`msginit`, `msgmerge`) and [`dprint`].

On Debian and Ubuntu, you can install Gettext with:

```shell
sudo apt install gettext
```

On MacOS with [Homebrew](https://brew.sh/), you can install with:

```shell
brew install gettext
```

### `dprint`

Install [`dprint`] using their installation instructions.

[`dprint`]: https://dprint.dev/

Ensure you can build the book, and that `mdbook serve` works. For this, follow
the instructions in the [README](README.md).

## Creating and Updating Translations

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

You should never touch the auto-generated `po/messages.pot` file. You should
also not never 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](STYLE.md) 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:

```shell
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:

```shell
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`](https://github.com/mgeisler/cloud-translate) tool to
> quickly machine-translate a new translation. Install it with
>
> ```shell
> 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.

Next, please update the file `.github/labeler.yml` to include the new language:

```diff
+ 'translation/xx':
+ - po/xx.po
```

### Refreshing an Existing Translation

As the English text changes, translations gradually become outdated. The
translations contain a POT-Creation-Date header which tells you when they were
last updated with new English messages.

To update the `po/xx.po` file with new messages, first extract the English text
into a `po/messages.pot` template file. Then run

```shell
msgmerge --update po/xx.po po/messages.pot
```

Notice that the POT-Creation-Date field is updated to the current time and date.
This becomes the new baseline for the translation: new English text added
afterwards will not show up in your translation, including completely new pages.

When running `msgmerge`, unchanged messages stay intact, deleted messages are
marked as old, and updated messages are marked "fuzzy". A fuzzy entry is not
used when we publish a translation! You have to go over the fuzzy entries by
hand and verify that the translation is correct 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.

### Editing a Translation

You should install a PO editor to edit the `.po` file for your language. The
files are simple text files, but it helps to use a dedicated editor since it
will take care of escaping things like `"` correctly.

There are many PO editors available. [Poedit](https://poedit.net/) is a popular
cross-platform choice, but you can also find several online editors.

### Formatting a Translation

If the file is not formatted correct, you will get an error on the PR. Make sure
to follow the [steps](#preparation) to install [Gettext] and
[`dprint`](https://dprint.dev/) and then run:

```shell
dprint fmt po/xx.po
```

This will automatically format the `.po` file for you. Commit the formatting fix
and push to your branch. Your PR should now be error free.

## 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`](https://github.com/mgeisler/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:

```shell
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:

```shell
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](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/commenting-on-a-pull-request).
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](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/incorporating-feedback-in-your-pull-request)
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.

[CODEOWNERS]: https://github.com/google/comprehensive-rust/blob/main/.github/CODEOWNERS