Internationalization

What is internationalization? What is internationalization?

Internationalization is the process of developing your theme, so it can easily be translated into other languages. Internationalization is often abbreviated as i18n (because there are 18 letters between the i and the n).

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Why is internationalization important? Why is internationalization important?

WordPress is used all over the world, and it is a good idea to prepare WordPress themes so that they can be easily translated into other languages. As a developer, you may not have an easy time providing localizations for all your users, but any translator can successfully localize the theme without modifying the source code itself.

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How to internationalize your theme? How to internationalize your theme?

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. Note that if you look online, you’ll see the _() function, which refers to the native PHP gettext-compliant translation function, but instead 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.

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Text Domains Text Domains

You need to use a text domain to denote all text belonging to that theme. 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 theme. If your theme’s name My Theme is defined in the style.css or it is contained in a folder called my-theme the domain name should be my-theme. The text domain name must use dashes and not underscores and be lowercase.

String example:

__( 'text', 'text-domain' );

 

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

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

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

Header example:

/*
* Theme Name: My Theme
* Author: Theme Author
* Text Domain: my-theme
*/

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Domain Path Domain Path

The domain path is used so WordPress knows where to find the translation when the theme is disabled.

Only useful if the translations are located in a language folder that is named something other than languages. For example, if .mo files are located in the languages folder then Domain Path will be /languages and must be written with the first slash. Defaults to the languages folder in the theme.

Header example:

/*
* Theme Name: My Theme
* Author: Theme Author
* Text Domain: my-theme
* Domain Path: /languages
*/

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Basic strings Basic strings

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

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

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

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

you can use the shorter:

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

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Variables Variables

If you are using variables in strings, similar to the example below, you need to use placeholders.

echo 'Your city is $city.'

Use the printf family of functions. Especially helpful are printf and sprintf. For example:

printf(
__( 'Your city is %s.', 'my-theme' ),
$city
);

Notice that the string for translation is the template "Your city is %s.", which is the same in both 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 (") tell php to interpret the $s as the s variable, which is not what we want.

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

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

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

The following example tells you what not to do

Warning: This is incorrect.

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

The strings for translation are extracted from the source without executing the PHP associated with it. For example: The variable $city may be Vancouver, so your string will read "Your city is Vancouver" when the template is run but gettext won’t know what is inside the PHP variable in advance.

As the value of the variable is unknown when your string is translated, it would require the translator to know every case for the variable $country. This is not ideal, and it is best to remove dynamic content and allow translators to focus on static content.

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Plurals Plurals

Basic Pluralization Basic Pluralization

If you have a 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(
'One comment',
'%s comments',
get_comments_number(),
'my-theme'
),
number_format_i18n( get_comments_number() )
);

_n() accepts 4 arguments:

  • singular – the singular form of the string
  • 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 theme’s text domain

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

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Pluralization done later Pluralization done later

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

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

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-theme'
),
number_format_i18n( get_comments_number() )
);

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Disambiguation by context Disambiguation by context

Sometimes a term is used in more than one context and must be translated separately in other languages, even though the same word is used for each context in English. 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-theme' );
_x( 'post', 'verb', 'my-theme' );

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

Taking an example from the German version of WordPress as an illustration: Post is Beiträge. The corresponding verb form in German is beitragen.

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

_ex( 'Post', 'noun', 'my-theme' );
_ex( 'post', 'verb', 'my-theme' );

Use the one you feel enhances legibility and ease of coding.

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Descriptions Descriptions

You can add a clarifying comment in the source code, so translators know how to translate a string like __( 'g:i:s a' ) . It must start with the words translators: and 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' );

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Newline characters Newline characters

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

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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 translators won’t have 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.

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Handling JavaScript files Handling JavaScript files

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

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Escaping strings Escaping strings

It is good to escape all of your strings, preventing translators from running malicious code. There are a few escape functions that are integrated with internationalization functions.

<a title="<?php esc_attr_e( 'Skip to content', 'my-theme' ); ?>" class="screen-reader-text skip-link" href="#content" >
  <?php _e( 'Skip to content', 'my-theme' ); ?>
</a>
<label for="nav-menu">
  <?php esc_html_e( 'Select Menu:', 'my-theme' ); ?>
</label>

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Localization functions Localization functions

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Basic functions Basic functions

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Translate & Escape functions Translate & Escape functions

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

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Date and number functions Date and number functions

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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 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-theme' ),
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-theme' ),
    $city,
    $zipcode
    );
    

    is always better than

    __( 'Your city is ', 'my-theme' ) . $city . __( ', and your zip code is ', 'my-theme' ) . $zipcode;
    
  • Try to use the same words and symbols to prevent translating multiple similar strings (e.g. don’t do the following)
    __( 'Posts:', 'my-theme' ); and __( 'Posts', 'my-theme' );
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    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( 'One post', '%s posts', $count )

      should become

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

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    Loading Text Domain Loading Text Domain

    You need to load the MO file with your theme’s translations. You can load them by calling the function load_theme_textdomain(). This call loads {locale}.mo from your theme’s base directory or {text-domain}-{locale}.mo from the WordPress theme language folder.

    The locale is the language code and/or country code you defined in the constant WPLANG in the file wp-config.php. For example, the locale for German is de_DE. So the code need for wp-config.php would be define ('WPLANG', 'de_DE');. For more information about language and country codes, see WordPress in Your Language.

    Watch Out

    • Name your MO file as {locale}.mo (e.g. de_DE.po & de_DE.mo) if adding the the translation to the theme folder.
    • Name your MO file as {text-domain}-{locale}.mo (e.g my-theme-de_DE.po & my-theme-de_DE.mo) if you are adding the translation to the WordPress theme language folder.

    Example:

    function my_theme_load_theme_textdomain() {
    load_theme_textdomain( 'my-theme', get_template_directory() . '/languages' );
    }
    add_action( 'after_setup_theme', 'my_theme_load_theme_textdomain' );
    

    This function should ideally be ran within the themes’ function.php

    Note:

    After WordPress 4.6 came out, translations now take translate.wordpress.org as priority and so themes that are translated via translate.wordpress.org do not necessary require load_theme_textdomain() anymore. However, there is no harm leaving that line in.

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