l10n: Update wp_get_installed_translations() to support variants of a language.

* A variant of a language has its own locale, for example the locale of the formal variant of German is `de_DE_formal`.
* Update `remove_accents()` and some CSS rules to support `de_DE_formal`.
* Add tests for `get_bloginfo( 'language' )`.
* API changes will be deployed over the next few days.

see #28303.

git-svn-id: https://develop.svn.wordpress.org/trunk@33027 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/formatting/BlogInfo.php

@@ -0,0 +1,34 @@
+<?php
+
+/**
+ * @group formatting
+ */
+class Tests_Formatting_BlogInfo extends WP_UnitTestCase {
+
+	/**
+	 * @dataProvider locales
+	 * @ticket 28303
+	 */
+	function test_get_bloginfo_language( $test_locale, $expected ) {
+		global $locale;
+
+		$old_locale = $locale;
+
+		$locale = $test_locale;
+		$this->assertEquals( $expected, get_bloginfo( 'language' ) );
+
+		$locale = $old_locale;
+	}
+
+	function locales() {
+		return array(
+			//     Locale          Language code
+			array( 'en_US',        'en-US' ),
+			array( 'ar',           'ar' ),
+			array( 'de_DE',        'de-DE' ),
+			array( 'de_DE_formal', 'de-DE-formal' ),
+			array( 'oci',          'oci' ),
+			array( 'pt_PT_ao1990', 'pt-PT-ao1990' ),
+		);
+	}
+}