diff --git a/MultisiteLanguageSwitcher.php b/MultisiteLanguageSwitcher.php
index ecb941be..69c63b8c 100644
--- a/MultisiteLanguageSwitcher.php
+++ b/MultisiteLanguageSwitcher.php
@@ -76,6 +76,11 @@ function get_the_msls( $attr ): string {
 	 * @uses get_the_msls
 	 *
 	 * @param string[] $arr
+	public static function init(): void
+	{
+		add_filter( 'the_content', array( $obj, 'content_filter' ) );
+
+	}
 	 */
 	function the_msls( array $arr = array() ): void {
 		echo get_the_msls( $arr );
diff --git a/includes/MslsContentFilter.php b/includes/MslsContentFilter.php
new file mode 100644
index 00000000..e91bf78f
--- /dev/null
+++ b/includes/MslsContentFilter.php
@@ -0,0 +1,76 @@
+<?php
+
+namespace lloc\Msls;
+
+class MslsContentFilter {
+
+
+	protected MslsOptions $options;
+
+	public function __construct( MslsOptions $options ) {
+		$this->options = $options;
+	}
+
+	/**
+	 * @codeCoverageIgnore
+	 */
+	public static function init(): void {
+		$obj = new self( msls_options() );
+
+		add_filter( 'the_content', array( $obj, 'content_filter' ) );
+	}
+
+	/**
+	 * Filter for the_content()
+	 *
+	 * @param string $content
+	 *
+	 * @return string
+	 */
+	public function content_filter( string $content ) {
+		if ( ! is_front_page() && is_singular() && $this->options->is_content_filter() ) {
+			$content .= $this->filter_string();
+		}
+
+		return $content;
+	}
+
+	/**
+	 * Create filter-string for msls_content_filter()
+	 *
+	 * @param string $pref
+	 * @param string $post
+	 *
+	 * @return string
+	 */
+	public function filter_string( $pref = '<p id="msls">', $post = '</p>' ) {
+		$obj   = MslsOutput::init();
+		$links = $obj->get( 1, true, true );
+
+		/* translators: %s: list of languages */
+		$output = __( 'This post is also available in %s.', 'multisite-language-switcher' );
+
+		if ( has_filter( 'msls_filter_string' ) ) {
+			/**
+			 * Overrides the string for the output of the translation hint
+			 *
+			 * @param string $output
+			 * @param array $links
+			 *
+			 * @since 1.0
+			 */
+			$output = apply_filters( 'msls_filter_string', $output, $links );
+		} elseif ( count( $links ) > 1 ) {
+			$last = array_pop( $links );
+
+			/* translators: %1$s: list of languages separated by a comma, %2$s: last language */
+			$format = __( '%1$s and %2$s', 'multisite-language-switcher' );
+
+			$output = sprintf( $output, sprintf( $format, implode( ', ', $links ), $last ) );
+		} elseif ( 1 == count( $links ) ) {
+			$output = sprintf( $output, $links[0] );
+		}
+
+		return ! empty( $output ) ? $pref . $output . $post : '';
+	}
+}
diff --git a/includes/MslsPlugin.php b/includes/MslsPlugin.php
index c5366ae8..497ac1e4 100644
--- a/includes/MslsPlugin.php
+++ b/includes/MslsPlugin.php
@@ -49,11 +49,11 @@ public static function init() {
 			add_action( 'init', array( MslsAdminBar::class, 'init' ) );
 			add_action( 'init', array( MslsBlock::class, 'init' ) );
 			add_action( 'init', array( MslsShortCode::class, 'init' ) );
+			add_action( 'init', array( MslsContentFilter::class, 'init' ) );
 			add_action( 'widgets_init', array( MslsWidget::class, 'init' ) );
 			add_action( 'wp_head', array( __CLASS__, 'print_alternate_links' ) );
 
 			add_filter( 'msls_get_output', array( __CLASS__, 'get_output' ) );
-			add_filter( 'the_content', array( $obj, 'content_filter' ) );
 
 			\lloc\Msls\ContentImport\Service::instance()->register();
 
@@ -127,70 +127,6 @@ public static function print_alternate_links() {
 		echo self::get_output()->get_alternate_links(), PHP_EOL;
 	}
 
-	/**
-	 * Filter for the_content()
-	 *
-	 * @param string $content
-	 *
-	 * @return string
-	 */
-	public function content_filter( string $content ) {
-		if ( ! is_front_page() && is_singular() && $this->options->is_content_filter() ) {
-			$content .= $this->filter_string();
-		}
-
-		return $content;
-	}
-
-	/**
-	 * Create filter-string for msls_content_filter()
-	 *
-	 * @param string $pref
-	 * @param string $post
-	 *
-	 * @return string
-	 */
-	public function filter_string( $pref = '<p id="msls">', $post = '</p>' ) {
-		$obj   = MslsOutput::init();
-		$links = $obj->get( 1, true, true );
-
-		/* translators: %s: list of languages */
-		$output = __( 'This post is also available in %s.', 'multisite-language-switcher' );
-
-		if ( has_filter( 'msls_filter_string' ) ) {
-			/**
-			 * Overrides the string for the output of the translation hint
-			 *
-			 * @param string $output
-			 * @param array $links
-			 *
-			 * @since 1.0
-			 */
-			$output = apply_filters( 'msls_filter_string', $output, $links );
-		} elseif ( count( $links ) > 1 ) {
-				$last = array_pop( $links );
-
-				/* translators: %1$s: list of languages separated by a comma, %2$s: last language */
-				$format = __( '%1$s and %2$s', 'multisite-language-switcher' );
-
-				$output = sprintf(
-					$output,
-					sprintf(
-						$format,
-						implode( ', ', $links ),
-						$last
-					)
-				);
-		} elseif ( 1 == count( $links ) ) {
-			$output = sprintf(
-				$output,
-				$links[0]
-			);
-		}
-
-		return ! empty( $output ) ? $pref . $output . $post : '';
-	}
-
 	/**
 	 * Loads styles and some js if needed
 	 *
diff --git a/tests/phpunit/TestMslsContentFilter.php b/tests/phpunit/TestMslsContentFilter.php
new file mode 100644
index 00000000..6c1ac81a
--- /dev/null
+++ b/tests/phpunit/TestMslsContentFilter.php
@@ -0,0 +1,76 @@
+<?php declare( strict_types=1 );
+
+namespace lloc\MslsTests;
+
+use Brain\Monkey\Functions;
+use lloc\Msls\MslsBlog;
+use lloc\Msls\MslsBlogCollection;
+use lloc\Msls\MslsContentFilter;
+use lloc\Msls\MslsOptions;
+
+use lloc\Msls\MslsPlugin;
+
+class TestMslsContentFilter extends MslsUnitTestCase {
+
+	protected function provide_content_filter_data(): array {
+		return array(
+			array( 'Test', 'Test', true, false, false ),
+			array( 'Test', 'Test', false, false, false ),
+			array( 'Test', 'Test', false, true, false ),
+			array( 'Test', 'Test', false, false, true ),
+			array( 'Test', 'Test', true, true, true ),
+		);
+	}
+
+	/**
+	 * @dataProvider provide_content_filter_data
+	 */
+	public function test_content_filter_empty( string $content, string $expected, bool $is_front_page, bool $is_singular, bool $is_content_filter ) {
+		Functions\when( 'is_front_page' )->justReturn( $is_front_page );
+		Functions\when( 'is_singular' )->justReturn( $is_singular );
+
+		$options = \Mockery::mock( MslsOptions::class );
+		$options->shouldReceive( 'is_content_filter' )->andReturn( $is_content_filter );
+
+		$test = new MslsContentFilter( $options );
+
+		$this->assertEquals( $expected, $test->content_filter( $content ) );
+	}
+
+	public function test_content_filter_one_link() {
+		$blog = \Mockery::mock( MslsBlog::class );
+		$blog->shouldReceive( 'get_language' )->once()->andReturn( 'de_DE' );
+		$blog->shouldReceive( 'get_description' )->once()->andReturn( 'Deutsch' );
+
+		$collection = \Mockery::mock( MslsBlogCollection::class );
+		$collection->shouldReceive( 'get_filtered' )->once()->andReturn( array( $blog ) );
+		$collection->shouldReceive( 'is_current_blog' )->once()->andReturn( true );
+
+		$options = \Mockery::mock( MslsOptions::class );
+		$options->shouldReceive( 'is_content_filter' )->andReturn( true );
+		$options->shouldReceive( 'get_flag_url' )->once()->andReturn( 'https://lloc.de/wp-content/plugins/msls/flags/de.png' );
+
+		Functions\expect( 'is_front_page' )->twice()->andReturn( false );
+		Functions\expect( 'is_admin' )->once()->andReturn( false );
+		Functions\expect( 'is_search' )->once()->andReturn( false );
+		Functions\expect( 'is_404' )->once()->andReturn( false );
+		Functions\expect( 'is_category' )->once()->andReturn( false );
+		Functions\expect( 'is_tag' )->once()->andReturn( false );
+		Functions\expect( 'is_tax' )->once()->andReturn( false );
+		Functions\expect( 'is_date' )->once()->andReturn( false );
+		Functions\expect( 'is_author' )->once()->andReturn( false );
+		Functions\expect( 'is_post_type_archive' )->once()->andReturn( false );
+		Functions\expect( 'get_queried_object_id' )->once()->andReturn( 42 );
+		Functions\expect( 'get_option' )->once()->andReturn( array() );
+		Functions\expect( 'is_singular' )->once()->andReturn( true );
+		Functions\expect( 'msls_options' )->once()->andReturn( $options );
+		Functions\expect( 'msls_blog_collection' )->once()->andReturn( $collection );
+		Functions\expect( 'get_permalink' )->once()->andReturn( 'https://msls.co/testpage/' );
+
+		$test = new MslsContentFilter( $options );
+
+		$content  = '<p>Test>/p>';
+		$expected = '<p>Test>/p><p id="msls">This post is also available in <a href="https://msls.co/testpage/" title="Deutsch" class="current_language">Deutsch</a>.</p>';
+		$this->assertEquals( $expected, $test->content_filter( $content ) );
+	}
+}
diff --git a/tests/phpunit/TestMslsPlugin.php b/tests/phpunit/TestMslsPlugin.php
index 786d229a..34c767cb 100644
--- a/tests/phpunit/TestMslsPlugin.php
+++ b/tests/phpunit/TestMslsPlugin.php
@@ -146,31 +146,6 @@ public function test_print_alternate_links() {
 		MslsPlugin::print_alternate_links();
 	}
 
-	protected function provide_content_filter_data(): array {
-		return array(
-			array( 'Test', 'Test', true, false, false ),
-			array( 'Test', 'Test', false, false, false ),
-			array( 'Test', 'Test', false, true, false ),
-			array( 'Test', 'Test', false, false, true ),
-			array( 'Test', 'Test', true, true, true ),
-		);
-	}
-
-	/**
-	 * @dataProvider provide_content_filter_data
-	 */
-	public function test_content_filter_empty( string $content, string $expected, bool $is_front_page, bool $is_singular, bool $is_content_filter ) {
-		Functions\when( 'is_front_page' )->justReturn( $is_front_page );
-		Functions\when( 'is_singular' )->justReturn( $is_singular );
-
-		$options = \Mockery::mock( MslsOptions::class );
-		$options->shouldReceive( 'is_content_filter' )->andReturn( $is_content_filter );
-
-		$test = new MslsPlugin( $options );
-
-		$this->assertEquals( $expected, $test->content_filter( $content ) );
-	}
-
 	public function test_activate(): void {
 		Functions\expect( 'register_uninstall_hook' )->once();