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How to Internationalize Your Plugin

Topics

In order to make a string translatable in your application you have to wrap the original strings in a call to one of a set of special functions.

Introduction to Gettext Introduction to Gettext

WordPress uses the gettext libraries and tools for i18n. If you look online, you’ll see the _() function which refers to the native PHP gettext-compliant translation function. With WordPress you should use the __() WordPress defined PHP function. If you want to get a broader and deeper view of gettext, we recommend you read the gettext online manual.

Text Domains Text Domains

Note:
After WordPress 4.6 came out, the Text Domain header is no longer required if it’s the same as the plugin slug. It’s now the default value.

It’s important to use a text domain to denote all text belonging to that plugin. The text domain is a unique identifier, which makes sure WordPress can distinguish between all loaded translations. This increases portability and plays better with already existing WordPress tools. The text domain must match the slug of the plugin. If your plugin is a single file called my-plugin.php or it is contained in a folder called my-plugin the domain name should be my-plugin. If your plugin is hosted on wordpress.org it must be the slug of your plugin URL (wordpress.org/plugins/<slug>).
The text domain name must use dashes and not underscores.

String example:

__( 'String (text to be internationalized)', 'text-domain' );

Change “text-domain” to the slug of your plugin.

Warning: Do not use variable names or constants for the text domain portion of a gettext function. Do not do this as a shortcut: __( ‘Translate me.’ , $text_domain );

The text domain also needs to be added to the plugin header. WordPress uses it to internationalize your plugin meta-data even when the plugin is disabled. The text domain should be same as the one used when loading the text domain.

Header example:

/*
 * Plugin Name: My Plugin
 * Author: Plugin Author
 * Text Domain: my-plugin
 */

Domain Path Domain Path

Note:
The Domain Path header can be omitted if the plugin is in the official WordPress Plugin Directory.

The domain path is used so that WordPress knows where to find the translation when the plugin is disabled. Only useful if the translations are located in a separate language folder because it defaults to the base folder the plugin is located in.

For example, if .mo files are located in the languages folder within your plugin then Domain Path will be “/languages” and must be written with the first slash:

Header example:

/*
 * Plugin Name: My Plugin
 * Author: Plugin Author
 * Text Domain: my-plugin
 * Domain Path: /languages
 */

Basic strings Basic strings

The most commonly used one is __(). It just returns the translation of its argument:

__( 'Blog Options', 'my-plugin' );

Another simple one is _e(), which outputs the translation of its argument. Instead of writing:

echo __( 'WordPress is the best!', 'my-plugin' );

you can use the shorter:

_e( 'WordPress is the best!', 'my-plugin' );

Variables Variables

If you are using variables in strings like in the example below you would use placeholders.

echo 'Your city is $city.'

The solution is to use the printf family of functions. Especially helpful are printf and sprintf. Here is what the right solution looks like:

printf(
	/* translators: %s: Name of a city */
	__( 'Your city is %s.', 'my-plugin' ),
	$city
);

Notice that here the string for translation is just the template "Your city is %s.", which is the same both in the source and at run-time.

If you have more than one placeholder in a string, it is recommended that you use argument swapping. In this case, single quotes (') are mandatory : double quotes (") will tell php to interpret the $s as the s variable, which is not what we want.

printf(
	/* translators: 1: Name of a city 2: ZIP code */
	__( 'Your city is %1$s, and your zip code is %2$s.', 'my-plugin' ),
	$city,
	$zipcode
);

Here the zip code is being displayed after the city name. In some languages displaying the zip code and city in opposite order would be more appropriate. Using %s prefix in the above example, allows for such a case. A translation can thereby be written:

printf(
	/* translators: 1: Name of a city 2: ZIP code */
	__( 'Your zip code is %2$s, and your city is %1$s.', 'my-plugin' ),
	$city,
	$zipcode
);

Important! This code is incorrect.

// This is incorrect do not use.
_e( "Your city is $city.", 'my-plugin' );

The strings for translation are extracted from the sources, so the translators will get this phrase to translate: "Your city is $city.".

However in the application _e will be called with an argument like "Your city is London." and gettext won’t find a suitable translation of this one and will return its argument: "Your city is London.". Unfortunately, it isn’t translated correctly.

Plurals Plurals

Basic Pluralization Basic Pluralization

If you have string that changes when the number of items changes. In English you have "One comment" and "Two comments". In other languages you can have multiple plural forms. To handle this in WordPress you can use the _n() function.

printf(
	_n(
		'%s comment',
		'%s comments',
		get_comments_number(),
		'my-plugin'
	),
	number_format_i18n( get_comments_number() )
);

_n() accepts 4 arguments:

singular – the singular form of the string (note that it can be used for numbers other than one in some languages, so '%s item' should be used instead of 'One item')
plural – the plural form of the string
count – the number of objects, which will determine whether the singular or the plural form should be returned (there are languages, which have far more than 2 forms)
text domain – the plugins text domain

The return value of the functions is the correct translated form, corresponding to the given count.

Pluralization done later Pluralization done later

You first set the plural strings with _n_noop() or _nx_noop().

$comments_plural = _n_noop(
	'%s comment.',
	'%s comments.'
);

Then at a later point in the code you can use translate_nooped_plural() to load the strings.

printf(
	translate_nooped_plural(
		$comments_plural,
		get_comments_number(),
		'my-plugin'
	),
	number_format_i18n( get_comments_number() )
);

Disambiguation by context Disambiguation by context

Sometimes one term is used in several contexts and although it is one and the same word in English it has to be translated differently in other languages. For example the word Post can be used both as a verb "Click here to post your comment" and as a noun "Edit this post". In such cases the _x() or _ex() function should be used. It is similar to __() and _e(), but it has an additional argument — the context:

_x( 'Post', 'noun', 'my-plugin' );
_x( 'Post', 'verb', 'my-plugin' );

Using this method in both cases we will get the string Comment for the original version, but the translators will see two Comment strings for translation, each in the different contexts.

Note that similarly to __(), _x() has an echo version: _ex(). The previous example could be written as:

_ex( 'Post', 'noun', 'my-plugin' );
_ex( 'Post', 'verb', 'my-plugin' );

Use whichever you feel enhances legibility and ease-of-coding.

Descriptions Descriptions

So that translators know how to translate a string like __( 'g:i:s a' ) you can add a clarifying comment in the source code. It has to start with the words translators: and to be the last PHP comment before the gettext call. Here is an example:

/* translators: draft saved date format, see http://php.net/date */
$saved_date_format = __( 'g:i:s a' );

It’s also used to explain placeholders in a string like _n_noop( '<strong>Version %1$s</strong> addressed %2$s bug.','<strong>Version %1$s</strong> addressed %2$s bugs.' ).

/* translators: 1: WordPress version number, 2: plural number of bugs. */
_n_noop( '<strong>Version %1$s</strong> addressed %2$s bug.',
         '<strong>Version %1$s</strong> addressed %2$s bugs.' );

Newline characters Newline characters

Gettext doesn’t like \r (ASCII code: 13) in translatable strings, so please avoid it and use \n instead.

Empty strings Empty strings

The empty string is reserved for internal Gettext usage and you must not try to internationalize the empty string. It also doesn’t make any sense, because the translators won’t see any context.

If you have a valid use-case to internationalize an empty string, add context to both help translators and be in peace with the Gettext system.

Handling JavaScript files Handling JavaScript files

Use wp_localize_script() to add translated strings or other server-side data to a previously enqueued script.

Escaping strings Escaping strings

It is good to escape all of your strings, this way the translators cannot run malicious code. There are a few escape functions that are integrated with internationalisation functions.

Localization functions Localization functions

Basic functions Basic functions

Translate & Escape functions Translate & Escape functions

Strings that require translation and is used in attributes of html tags must be escaped.

Date and number functions Date and number functions

Best Practices for writing strings Best Practices for writing strings

Here are the best practices for writing strings

Use decent English style – minimize slang and abbreviations.
Use entire sentences – in most languages word order is different than that in English.
Split at paragraphs – merge related sentences, but do not include a whole page of text in one string.
Do not leave leading or trailing whitespace in a translatable phrase.
Assume strings can double in length when translated
Avoid unusual markup and unusual control characters – do not include tags that surround your text
Do not put unnecessary HTML markup into the translated string
Do not leave URLs for translation, unless they could have a version in another language.
Add the variables as placeholders to the string as in some languages the placeholders change position.

printf(
	__( 'Search results for: %s', 'my-plugin' ),
	get_search_query()
);

Use format strings instead of string concatenation – translate phrases and not words –

printf(
    __( 'Your city is %1$s, and your zip code is %2$s.', 'my-plugin' ),
    $city,
    $zipcode
);

is always better than:

__( 'Your city is ', 'my-plugin' ) . $city . __( ', and your zip code is ', 'my-plugin' ) . $zipcode;

Try to use the same words and same symbols so not multiple strings needs to be translated e.g.__( 'Posts:', 'my-plugin' ); and __( 'Posts', 'my-plugin' );

Add Text Domain to strings Add Text Domain to strings

You must add your Text domain as an argument to every __(), _e() and __n() gettext call, or your translations won’t work.

Examples:

```
__( 'Post' )
```
should become
```
__( 'Post', 'my-theme' )
```
```
_e( 'Post' )
```
should become
```
_e( 'Post', 'my-theme' )
```

_n( '%s post', '%s posts', $count )

should become

_n( '%s post', '%s posts', $count, 'my-theme' )

If there are strings in your plugin that are also used in WordPress core (e.g. ‘Settings’), you should still add your own text domain to them, otherwise they’ll become untranslated if the core string changes (which happens).

Adding the text domain by hand can be a burden if not done continuously when writing code and that’s why you can do it automatically:

Download the add-textdomain.php script to the folder where the file is you want to add the text domain
In command line move to the directory where the file is
Run this command to create a new file with the text domain added

php add-textdomain.php my-plugin my-plugin.php > new-my-plugin.php

If you wish to have the add-textdomain.php in a different folder you just need to define the location in the command.

php \path\to\add-textdomain.php my-plugin my-plugin.php > new-my-plugin.php

Use this command if you don’t want a new file outputted.

php add-textdomain.php -i my-plugin my-plugin.php

If you want to change multiple files in a directory you can also pass a directory to the script.

php add-textdomain.php -i my-plugin my-plugin-directory

After it’s done, the text domain will be added to the end of all gettext calls in the file. If there is an existing text domain it will not be replaced.

Loading Text Domain Loading Text Domain

Note:
After WordPress 4.6 came out, translations now take translate.wordpress.org as priority and so plugins that are translated via translate.wordpress.org do not necessary require load_plugin_textdomain() anymore.
If you don’t want to add a load_plugin_textdomain() call to your plugin you have to set the Requires at least: field in your readme.txt to 4.6.

You need to load the MO file with your plugin’s translations. You can load them by calling the function load_plugin_textdomain(). This call loads {text-domain}-{locale}.mo from your plugin’s base directory. The locale is the language code and/or country code of the site language setting under General Settings. For more information about language and country codes, see WordPress in Your Language.

From the code example above the text domain is my-plugin therefore the German MO and PO files should be named my-plugin-de_DE.mo and my-plugin-de_DE.po.
Example:

function my_plugin_load_plugin_textdomain() {
	load_plugin_textdomain( 'my-plugin', FALSE, basename( dirname( __FILE__ ) ) . '/languages/' );
}
add_action( 'plugins_loaded', 'my_plugin_load_plugin_textdomain' );

Language Packs Language Packs

If you’re interested in language packs and how the import to translate.wordpress.org is working, please read the Meta Handbook page about Translations.