Index: src/wp-includes/l10n.php
===================================================================
--- src/wp-includes/l10n.php	(revision 25564)
+++ src/wp-includes/l10n.php	(working copy)
@@ -27,6 +27,13 @@
 	global $locale;
 
 	if ( isset( $locale ) )
+		/**
+		 * Filter WordPress install's locale ID.
+		 *
+		 * @since 1.5.2
+		 *
+		 * @param string $locale The locale id.
+		 */
 		return apply_filters( 'locale', $locale );
 
 	// WPLANG is defined in wp-config.
@@ -46,6 +53,7 @@
 	if ( empty( $locale ) )
 		$locale = 'en_US';
 
+	// duplicate_hook
 	return apply_filters( 'locale', $locale );
 }
 
@@ -64,6 +72,15 @@
  */
 function translate( $text, $domain = 'default' ) {
 	$translations = get_translations_for_domain( $domain );
+	/**
+	 * Filter text with its translation.
+	 *
+	 * @since 2.0.11
+	 *
+	 * @param string $translations Translated text.
+	 * @param string $text         Text to translate.
+	 * @param string $domain       Text domain. Unique identifier for retrieving translated strings.
+	 */
 	return apply_filters( 'gettext', $translations->translate( $text ), $text, $domain );
 }
 
@@ -101,6 +118,16 @@
  */
 function translate_with_gettext_context( $text, $context, $domain = 'default' ) {
 	$translations = get_translations_for_domain( $domain );
+	/**
+	 * Filter text with its translation based on context information.
+	 *
+	 * @since 2.8.0
+	 *
+	 * @param string $translations Translated text.
+	 * @param string $text         Text to translate.
+	 * @param string $context      Context information for the translators.
+	 * @param string $domain       Text domain. Unique identifier for retrieving translated strings.
+	 */
 	return apply_filters( 'gettext_with_context', $translations->translate( $text, $context ), $text, $context, $domain );
 }
 
@@ -268,6 +295,17 @@
 function _n( $single, $plural, $number, $domain = 'default' ) {
 	$translations = get_translations_for_domain( $domain );
 	$translation = $translations->translate_plural( $single, $plural, $number );
+	/**
+	 * Filter text with its translation when plural option is available.
+	 *
+	 * @since 2.2.0
+	 *
+	 * @param string $translation Translated text.
+	 * @param string $single      The text that will be used if $number is 1.
+	 * @param string $plural      The text that will be used if $number is not 1.
+	 * @param string $number      The number to compare against to use either $single or $plural.
+	 * @param string $domain      Text domain. Unique identifier for retrieving translated strings.
+	 */
 	return apply_filters( 'ngettext', $translation, $single, $plural, $number, $domain );
 }
 
@@ -288,6 +326,18 @@
 function _nx($single, $plural, $number, $context, $domain = 'default') {
 	$translations = get_translations_for_domain( $domain );
 	$translation = $translations->translate_plural( $single, $plural, $number, $context );
+	/**
+	 * Filter text with its translation while plural option and context are available.
+	 *
+	 * @since 2.8.0
+	 *
+	 * @param string $translation Translated text.
+	 * @param string $single      The text that will be used if $number is 1.
+	 * @param string $plural      The text that will be used if $number is not 1.
+	 * @param string $number      The number to compare against to use either $single or $plural.
+	 * @param string $context     Context information for the translators.
+	 * @param string $domain      Text domain. Unique identifier for retrieving translated strings.
+	 */
 	return apply_filters( 'ngettext_with_context', $translation, $single, $plural, $number, $context, $domain );
 }
 
@@ -367,6 +417,15 @@
 function load_textdomain( $domain, $mofile ) {
 	global $l10n;
 
+	/**
+	 * Filter text domain and/or MO file path for loading translations.
+	 *
+	 * @since 2.9.0
+	 *
+	 * @param boolean        Whether to override the textomain. Default false.
+	 * @param string $domain Text domain. Unique identifier for retrieving translated strings.
+	 * @param string $mofile Path to the MO file.
+	 */
 	$plugin_override = apply_filters( 'override_load_textdomain', false, $domain, $mofile );
 
 	if ( true == $plugin_override ) {
@@ -375,6 +434,14 @@
 
 	do_action( 'load_textdomain', $domain, $mofile );
 
+	/**
+	 * Filter MO file path for loading translations for a specific text domain.
+	 *
+	 * @since 2.9.0
+	 *
+	 * @param string $mofile Path to the MO file.
+	 * @param string $domain Text domain. Unique identifier for retrieving translated strings.
+	 */
 	$mofile = apply_filters( 'load_textdomain_mofile', $mofile, $domain );
 
 	if ( !is_readable( $mofile ) ) return false;
@@ -401,6 +468,14 @@
 function unload_textdomain( $domain ) {
 	global $l10n;
 
+	/**
+	 * Filter text domain for loading translation.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param boolean        Whether to override unloading the text domain. Default false.
+	 * @param string $domain Text domain. Unique identifier for retrieving translated strings.
+	 */
 	$plugin_override = apply_filters( 'override_unload_textdomain', false, $domain );
 
 	if ( $plugin_override )
@@ -458,7 +533,16 @@
  * @param string $plugin_rel_path Optional. Relative path to WP_PLUGIN_DIR where the .mo file resides.
  */
 function load_plugin_textdomain( $domain, $deprecated = false, $plugin_rel_path = false ) {
-	$locale = apply_filters( 'plugin_locale', get_locale(), $domain );
+	$locale = get_locale();
+	/**
+	 * Filter a plugin's locale.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param string $locale The plugin's current locale.
+	 * @param string $domain Text domain. Unique identifier for retrieving translated strings.
+	 */
+	$locale = apply_filters( 'plugin_locale', $locale, $domain );
 
 	if ( false !== $plugin_rel_path	) {
 		$path = WP_PLUGIN_DIR . '/' . trim( $plugin_rel_path, '/' );
@@ -490,6 +574,7 @@
  * @return bool True when textdomain is successfully loaded, false otherwise.
  */
 function load_muplugin_textdomain( $domain, $mu_plugin_rel_path = '' ) {
+	// duplicate_hook
 	$locale = apply_filters( 'plugin_locale', get_locale(), $domain );
 	$path = trailingslashit( WPMU_PLUGIN_DIR . '/' . ltrim( $mu_plugin_rel_path, '/' ) );
 
@@ -519,7 +604,16 @@
  * @return bool True when textdomain is successfully loaded, false otherwise.
  */
 function load_theme_textdomain( $domain, $path = false ) {
-	$locale = apply_filters( 'theme_locale', get_locale(), $domain );
+	$locale = get_locale();
+	/**
+	 * Filter a theme's locale.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param string $locale The theme's current locale.
+	 * @param string $domain Text domain. Unique identifier for retrieving translated strings.
+	 */
+	$locale = apply_filters( 'theme_locale', $locale, $domain );
 
 	if ( ! $path )
 		$path = get_template_directory();