Add is-installed command to check if a given language is installed

README.md

@@ -63,8 +63,6 @@ wp language core
 
 
 
-
-
 ### wp language core activate
 
 Activates a given language.
@@ -85,6 +83,30 @@ wp language core activate <language>
 
 
 
+### wp language core is-installed
+
+Checks if a given language is installed.
+
+~~~
+wp language core is-installed <language>
+~~~
+
+Returns exit code 0 when installed, 1 when uninstalled.
+
+**OPTIONS**
+
+	<language>
+		The language code to check.
+
+**EXAMPLES**
+
+    # Check whether the German language is installed; exit status 0 if installed, otherwise 1.
+    $ wp language core is-installed de_DE
+    $ echo $?
+    1
+
+
+
 ### wp language core install
 
 Installs a given language.

composer.json

@@ -37,6 +37,7 @@
             "language",
             "language core",
             "language core activate",
+            "language core is-installed",
             "language core install",
             "language core list",
             "language core uninstall",

features/language-core.feature

@@ -13,6 +13,14 @@ Feature: Manage translation files for a WordPress install
       | en_US     | English (United States) | active        |
       | en_GB     | English (UK)            | uninstalled   |
 
+    When I try `wp language core is-installed en_GB`
+    Then the return code should be 1
+    And STDERR should be empty
+
+    When I try `wp language core is-installed en_AU`
+    Then the return code should be 1
+    And STDERR should be empty
+
     When I run `wp language core install en_GB`
     And I run `wp language core install en_AU`
     Then the wp-content/languages/admin-en_GB.po file should exist
@@ -23,6 +31,12 @@ Feature: Manage translation files for a WordPress install
       """
     And STDERR should be empty
 
+    When I try `wp language core is-installed en_GB`
+    Then the return code should be 0
+
+    When I try `wp language core is-installed en_AU`
+    Then the return code should be 0
+
     When I run `wp language core install en_CA en_NZ`
     Then the wp-content/languages/admin-en_CA.po file should exist
     And the wp-content/languages/en_CA.po file should exist

src/WP_CLI/CommandWithTranslation.php

@@ -121,6 +121,38 @@ protected function sort_translations_callback( $a, $b ) {
 		return strnatcasecmp( $a['language'], $b['language'] );
 	}
 
+	/**
+	 * Checks if a given language is installed.
+	 *
+	 * Returns exit code 0 when installed, 1 when uninstalled.
+	 *
+	 * ## OPTIONS
+	 *
+	 * <language>
+	 * : The language code to check.
+	 *
+	 * ## EXAMPLES
+	 *
+	 *     # Check whether the German language is installed; exit status 0 if installed, otherwise 1.
+	 *     $ wp language core is-installed de_DE
+	 *     $ echo $?
+	 *     1
+	 *
+	 * @subcommand is-installed
+	 */
+	public function is_installed( $args, $assoc_args = array() ) {
+
+		list( $language_code ) = $args;
+
+		$available = $this->get_installed_languages();
+
+		if ( in_array( $language_code, $available, true ) ) {
+			\WP_CLI::halt( 0 );
+		} else {
+			\WP_CLI::halt( 1 );
+		}
+	}
+
 	/**
 	 * Installs a given language.
 	 *