Localizing WordPress Themes and Plugins

Now we get to the heart of this guide: localizing a theme or plugin. To demonstrate the techniques involved we will look at a file from the default WordPress theme, which is surprisingly not localized. The file is:


The exact same process involved in localizing a theme applies to plugins.

Text domains

The first step in preparing your theme or plugin is to decide on a text domain. A text domain is a way for you to separate your localized messages from localized messages in other themes and plugins, and from the rest of WordPress itself. A text domain is simply a text string that identifies your theme or plugin, and is typically the name of the theme or plugin (without any .php extension). Using the default theme as an example, we will chose a text domain of kubrick. Once we’ve chosen the domain we need to tell WordPress about it.

For plugins we insert the following function in an appropriate part of the plugin file and before any text is output:

load_plugin_textdomain ($domain);

Ideally this will be inserted after all other plugins have loaded to allow the best compatibility. This can be achieved by loading the domain in the init action.

add_action( 'init', 'my_plugin_init' );

function my_plugin_init() {
  load_plugin_textdomain( 'mydomain' );

For themes we insert the following function at the top of functions.php in the theme directory:

load_theme_textdomain ($domain);

Our theme or plugin is now setup to receive a localization. It is important to note that we must specify the text domain whenever we use the WordPress localization functions:

  • __($text, $domain) – Looks for a translated version of $text in text domain $domainand returns the result
  • _e($text, $domain) – Looks for a translated version of $text in text domain $domainand echo the result to the screen (i.e. effectively it is echo __($text))

If we do not specify the text domain then WordPress assumes the localization is contained within the core locale files.

Marking text strings

As we’ve already seen, marking a string is simply a case of wrapping it inside an appropriate WordPress function. Using the following highlighted version of index.php, we will look at individual pieces of text and explain how they should be marked.

<?php get_header(); ?>

<div id="content" class="narrowcolumn">

<?php if (have_posts()) : ?>

	<?php while (have_posts()) : the_post(); ?>

		<div class="post" id="post-<?php the_ID(); ?>">
				<a href="<?php the_permalink() ?>" rel="bookmark" 
					 title="Permanent Link to <?php the_title(); ?>">
					<?php the_title(); ?>
				<?php the_time('F jS, Y') ?> <!-- by <?php the_author() ?> -->

			<div class="entry">
				<?php the_content('Read the rest of this entry &raquo;'); ?>

			<p class="postmetadata">
				Posted in <?php the_category(', ') ?> | 
				<?php edit_post_link('Edit', '', ' | '); ?>  
				<?php comments_popup_link('No Comments &#187;', '1 Comment &#187;', 
																	'% Comments &#187;'); ?>

	<?php endwhile; ?>

	<div class="navigation">
		<div class="alignleft">
			<?php next_posts_link('&laquo; Previous Entries') ?>
		<div class="alignright">
			<?php previous_posts_link('Next Entries &raquo;') ?>

<?php else : ?>

	<h2 class="center">Not Found</h2>
	<p class="center">
		Sorry, but you are looking for something that isn't here.
	<?php include (TEMPLATEPATH . "/searchform.php"); ?>

<?php endif; ?>


<?php get_sidebar(); ?>

<?php get_footer(); ?>

First up is the title that appears when you hover over a link (from line 12):

Permanent Link to 

This uses the function the_title (), which displays the post title resulting in text such as ‘Permanent link to My First Post‘. Obviously we don’t want to localize every post title so we need to indicate that the post title is added at run-time. A simple first attempt at localizing this might look like:

<?php _e ('Permanent Link to', 'kubrick') ?> <?php the_title (); ?>

This would indeed produce the correct result of ‘Permanent Link to My First Post‘. However, it assumes that the localized language uses the same rules as English and that the subject ‘My First Post‘ will follow ‘Permanent Link to‘. This is not always the case and another language may need to reorder the words to look something like ‘My First Post is a permanent link‘. The translator may not actually be able to directly translate the English (the language or grammar may not support a similar concept) and could be required to dramatically change the meaning of the text, even to the point of removing the run-time title. This apparently simple line demonstrates the need to be careful about making assumptions based upon your own language.

A better attempt is:

<?php printf(__ ('Permanent Link to %s', 'kubrick'), get_the_title())?>&quot;>

Here we use the PHP function printf which allows us to insert run-time data. We pass this function the localized string ‘Permanent Link to %s‘, as well as the run-time value received from the function get_the_title () (remember that the_title displays the title, while get_the_title returns it to printf). The printf function will then insert the runtime title where the %s symbol is, resulting in a correct display and also allowing a translator to change the position of the run-time data in a localization:

msgid "Permanent Link to %s"
msgstr "%s is a permanent link"

Next we have the time display (line 17):

<?php the_time('F jS, Y') ?> 

Localizing time can be a complicated process and will be dealt with separately later. The important thing to remember here is that we need to give the translator the ability to change how the date and time is displayed as it is unlikely to be the same as in English.

<?php the_time(__ ('F jS, Y', 'kubrick')) ?> 

A simple line to display the post content (from line 21):

<?php the_content('Read the rest of this entry &amp;raquo;') ?>

In general you should always include punctuation in localized strings as this allows a translator to remove it when not appropriate. In this case the » symbol is included.

<?php the_content(__('Read the rest of this entry &amp;raquo;', 'kubrick'))?>

Next is a localization that requires some thought:

<?php comments_popup_link('No Comments &amp;#187;','1 Comment &amp;#187;','% Comments &amp;#187;'); ?>

The problem here is that while in English there are three variations of the phrase (for none, one, and more than one), some languages have more or less variations. The WordPress function comments_popup_link () only allows three to be specified, so how do we work around this? The answer for the first two variations is simple: we do nothing special:

__ ('No Comments &amp;#187;', 'kubrick'),
__ ('1 Comment &amp;#187;', 'kubrick')

The translator is able to localize this according to their language with no ill effects if they require more or less variations. The third case is different and we need to allow additional variations. WordPress provides us with a specific function called __ngettext. Details of this function will be given in the next section

__ngettext ('%d comment', '%d comments', get_comments_number (), 'kubrick')

This results in a final localization of:

<?php comments_popup_link(__ ('No Comments &amp;#187;', 'kubrick'), __ ('1 Comment &amp;#187;', 'kubrick'), __ngettext ('% comment', '% comments', get_comments_number (),'kubrick')); ?>


Plurals are tricky enough in English, and you cannot assume that other languages follow the same rules. Chinese, for example, requires no additional suffixes for plurals, while Czech has very complicated rules. Fortunately WordPress has already thought of this and you can localize plurals using the special function __ngettext:

<?php __ngettext ($single, $plural, $number, $domain); ?>

This function takes three parameters (as well as the domain).

  • $single – The text when $number is 1
  • $plural – The text when $number is greater than 1
  • $number – The actual number

In the following .PO file you can see how this would look in Czech:

msgid "%d window"
msgid_plural "%d windows"
msgstr[0] "0 oken"
msgstr[1] "1 okno"
msgstr[2] "2 okna"

Note how Czech has more cases than English.

Dates and times

Dates and times are one of the most tricky aspects of localization due to the variety of words, formatting, and positioning. Let’s look at a few possibilities to show how complicated the situation is.

  • US English – 4/28/2007
  • UK English – 28/4/2007
  • Chinese – 2005年2月27日

We can see that not only do we need to translate the words, but we also need to be able to change the position and change the formatting.

Most dates will be displayed using the PHP function date. This allows the date to be configured according to various format settings (see the PHP date page for full details). As such, any date format string should always be localized to allow a translator to modify it:

date ('l, F js, Y', 'myplugin');

However, this assumes that the host running your site will be configured in the appropriate locale. Typically this is not the case. To get around this problem WordPress provides an additional function that accepts a date format string, but internally translates any day or month strings for you.

mysql2date (__ ('l, F js, Y', 'myplugin'));

Numbers and currencies

Like dates and times, numbers and currencies are also very tricky. For example:

  • 1,000,000.53
  • 1.000.000,53
  • 1000000.53
  • $4.00
  • £4.00
  • 4 HK$

If you are displaying a lot of numbers and it is important to have the correct separators and currency formatting then you will need to devise your own method of allowing the user to configure the output. Typically this will include:

  • Number separator (1,000.50 or 1.000,50)
  • Currency symbol ($, £, ¢ etc)
  • Currency position (before, after, with or without space)

It should be noted that PHP provides a useful function number_format which will take a number and format it according to the parameters you specify:

number_format (1000.50, 2, '.', ',');

This will display the number 1000.50 to two decimal places using a period as the decimal separator and a comma to separate thousands. The output value will be 1,000.50.

Word order

Word order is not usually an issue until you start inserting multiple values at run-time. Consider the following phrase:

Today is %s and the weather is %s

This seems innocent enough. However, in another language the word order may need to be reversed. Without any additional help this would be impossible – even if we translated this to ‘The weather is %s and today is %s‘, the data that is inserted at run-time would still be in the wrong order (we would end up with ‘The weather is Sunday and today is sunny‘).

To cater for this you can use placeholders. A placeholder is similar to the existing printf-style strings, but also defines a place:

Today is %1$s and the weather is %2$s

Here we have defined that the first runtime parameter will contain the day, and the second runtime parameter will contain the weather. This can then be translated into whatever order is needed:

The weather is %2$s and today is %1$s

This time the correct run-time data will be inserted into the appropriate position.


Text messages in JavaScript also need to be localized. Without resorting to dynamically-generated JavaScript we can use a very simple techni