diff --git a/features/makejson.feature b/features/makejson.feature
index dc8ab19f..f5314ef5 100644
--- a/features/makejson.feature
+++ b/features/makejson.feature
@@ -325,15 +325,15 @@ Feature: Split PO files into JSON files.
       """
       "D"
       """
-    And the foo-plugin/foo-plugin-de_DE.po file should not contain:
+    And the foo-plugin/foo-plugin-de_DE.po file should contain:
       """
       "A"
       """
-    And the foo-plugin/foo-plugin-de_DE.po file should not contain:
+    And the foo-plugin/foo-plugin-de_DE.po file should contain:
       """
       "B"
       """
-    And the foo-plugin/foo-plugin-de_DE.po file should not contain:
+    And the foo-plugin/foo-plugin-de_DE.po file should contain:
       """
       "C"
       """
@@ -377,7 +377,7 @@ Feature: Split PO files into JSON files.
       msgstr "D"
       """
 
-    When I run `wp i18n make-json foo-plugin --no-purge`
+    When I run `wp i18n make-json foo-plugin`
     Then STDOUT should contain:
       """
       Success: Created 2 files.
@@ -437,104 +437,6 @@ Feature: Split PO files into JSON files.
       "C"
       """
 
-  Scenario: Does generate or update MO files
-    Given an empty foo-plugin directory
-    And a foo-plugin/foo-plugin-de_DE.po file:
-      """
-      # Copyright (C) 2018 Foo Plugin
-      # This file is distributed under the same license as the Foo Plugin package.
-      msgid ""
-      msgstr ""
-      "Project-Id-Version: Foo Plugin\n"
-      "Report-Msgid-Bugs-To: https://wordpress.org/support/plugin/foo-plugin\n"
-      "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
-      "Language-Team: LANGUAGE <LL@li.org>\n"
-      "Language: de_DE\n"
-      "MIME-Version: 1.0\n"
-      "Content-Type: text/plain; charset=UTF-8\n"
-      "Content-Transfer-Encoding: 8bit\n"
-      "POT-Creation-Date: 2018-05-02T22:06:24+00:00\n"
-      "PO-Revision-Date: 2018-05-02T22:06:24+00:00\n"
-      "X-Domain: foo-plugin\n"
-      "Plural-Forms: nplurals=2; plural=(n != 1);\n"
-
-      #: a.js:10
-      msgid "A"
-      msgstr "A"
-
-      #: b.js:10
-      msgid "B"
-      msgstr "B"
-
-      #: a.js:10
-      #: b.js:10
-      msgid "C"
-      msgstr "C"
-
-      #: foo-plugin.php:10
-      msgid "D"
-      msgstr "D"
-      """
-
-    When I run `wp i18n make-json foo-plugin`
-    Then STDOUT should contain:
-      """
-      Success: Created 2 files.
-      """
-    And the return code should be 0
-
-    And the foo-plugin/foo-plugin-de_DE-95f0a310f289230d56c3a4949c17963e.json file should exist
-    And the foo-plugin/foo-plugin-de_DE.mo file should exist
-
-  Scenario: Does not generate or update MO files
-    Given an empty foo-plugin directory
-    And a foo-plugin/foo-plugin-de_DE.po file:
-      """
-      # Copyright (C) 2018 Foo Plugin
-      # This file is distributed under the same license as the Foo Plugin package.
-      msgid ""
-      msgstr ""
-      "Project-Id-Version: Foo Plugin\n"
-      "Report-Msgid-Bugs-To: https://wordpress.org/support/plugin/foo-plugin\n"
-      "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
-      "Language-Team: LANGUAGE <LL@li.org>\n"
-      "Language: de_DE\n"
-      "MIME-Version: 1.0\n"
-      "Content-Type: text/plain; charset=UTF-8\n"
-      "Content-Transfer-Encoding: 8bit\n"
-      "POT-Creation-Date: 2018-05-02T22:06:24+00:00\n"
-      "PO-Revision-Date: 2018-05-02T22:06:24+00:00\n"
-      "X-Domain: foo-plugin\n"
-      "Plural-Forms: nplurals=2; plural=(n != 1);\n"
-
-      #: a.js:10
-      msgid "A"
-      msgstr "A"
-
-      #: b.js:10
-      msgid "B"
-      msgstr "B"
-
-      #: a.js:10
-      #: b.js:10
-      msgid "C"
-      msgstr "C"
-
-      #: foo-plugin.php:10
-      msgid "D"
-      msgstr "D"
-      """
-
-    When I run `wp i18n make-json foo-plugin --no-update-mo-files`
-    Then STDOUT should contain:
-      """
-      Success: Created 2 files.
-      """
-    And the return code should be 0
-
-    And the foo-plugin/foo-plugin-de_DE-95f0a310f289230d56c3a4949c17963e.json file should exist
-    And the foo-plugin/foo-plugin-de_DE.mo file should not exist
-
   Scenario: Correctly saves strings with context
     Given an empty foo-plugin directory
     And a foo-plugin/foo-plugin-de_DE.po file:
diff --git a/features/makemo.feature b/features/makemo.feature
index c1bff75d..ae0e2585 100644
--- a/features/makemo.feature
+++ b/features/makemo.feature
@@ -183,7 +183,7 @@ Feature: Generate MO files from PO files
       "X-Domain: foo-plugin\n"
       "Plural-Forms: nplurals=2; plural=(n != 1);\n"
 
-      #: foo-plugin.js:15
+      #: foo-plugin.php:15
       msgid "Foo Plugin"
       msgstr "Bar Plugin"
       """
@@ -198,3 +198,59 @@ Feature: Generate MO files from PO files
       """
       Bar Plugin
       """
+
+  Scenario: Excludes JS-only strings from MO files
+    Given an empty foo-plugin directory
+    And a foo-plugin/foo-plugin-de_DE.po file:
+      """
+      # Copyright (C) 2018 Foo Plugin
+      # This file is distributed under the same license as the Foo Plugin package.
+      msgid ""
+      msgstr ""
+      "Project-Id-Version: Foo Plugin\n"
+      "Report-Msgid-Bugs-To: https://wordpress.org/support/plugin/foo-plugin\n"
+      "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
+      "Language-Team: LANGUAGE <LL@li.org>\n"
+      "Language: de_DE\n"
+      "MIME-Version: 1.0\n"
+      "Content-Type: text/plain; charset=UTF-8\n"
+      "Content-Transfer-Encoding: 8bit\n"
+      "POT-Creation-Date: 2018-05-02T22:06:24+00:00\n"
+      "PO-Revision-Date: 2018-05-02T22:06:24+00:00\n"
+      "X-Domain: foo-plugin\n"
+      "Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+      #: foo-plugin.js:15
+      msgid "JS Only String"
+      msgstr "JS Only Translation"
+
+      #: foo-plugin.php:10
+      msgid "PHP String"
+      msgstr "PHP Translation"
+
+      #: foo-plugin.js:20
+      #: foo-plugin.php:15
+      msgid "Both JS and PHP"
+      msgstr "Both Translation"
+      """
+
+    When I run `wp i18n make-mo foo-plugin`
+    Then STDOUT should contain:
+      """
+      Success: Created 1 file.
+      """
+    And the return code should be 0
+    And the foo-plugin/foo-plugin-de_DE.mo file should exist
+    And the foo-plugin/foo-plugin-de_DE.mo file should contain:
+      """
+      PHP Translation
+      """
+    And the foo-plugin/foo-plugin-de_DE.mo file should contain:
+      """
+      Both Translation
+      """
+    And the foo-plugin/foo-plugin-de_DE.mo file should not contain:
+      """
+      JS Only Translation
+      """
+
diff --git a/features/makephp.feature b/features/makephp.feature
index d345dea4..66f12711 100644
--- a/features/makephp.feature
+++ b/features/makephp.feature
@@ -202,7 +202,15 @@ Feature: Generate PHP files from PO files
     And the return code should be 0
     And the foo-plugin/foo-plugin-de_DE.l10n.php file should contain:
       """
-      return ['domain'=>'foo-plugin','plural-forms'=>'nplurals=2; plural=(n != 1);','language'=>'de_DE','project-id-version'=>'Foo Plugin','pot-creation-date'=>'2018-05-02T22:06:24+00:00','po-revision-date'=>'2018-05-02T22:06:24+00:00','messages'=>['Plugin NameFoo Plugin (EN)'=>'Foo Plugin (DE)','Foo Plugin'=>'Bar Plugin','You have %d new message'=>'Sie haben %d neue Nachricht' . "\0" . 'Sie haben %d neue Nachrichten']];
+      You have %d new message
+      """
+    And the foo-plugin/foo-plugin-de_DE.l10n.php file should not contain:
+      """
+      Foo Plugin (DE)
+      """
+    And the foo-plugin/foo-plugin-de_DE.l10n.php file should not contain:
+      """
+      Bar Plugin
       """
 
   Scenario: Excludes strings without translations
@@ -300,3 +308,59 @@ Feature: Generate PHP files from PO files
       """
       	'messages' => [
       """
+
+  Scenario: Excludes JS-only strings from PHP files
+    Given an empty foo-plugin directory
+    And a foo-plugin/foo-plugin-de_DE.po file:
+      """
+      # Copyright (C) 2018 Foo Plugin
+      # This file is distributed under the same license as the Foo Plugin package.
+      msgid ""
+      msgstr ""
+      "Project-Id-Version: Foo Plugin\n"
+      "Report-Msgid-Bugs-To: https://wordpress.org/support/plugin/foo-plugin\n"
+      "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
+      "Language-Team: LANGUAGE <LL@li.org>\n"
+      "Language: de_DE\n"
+      "MIME-Version: 1.0\n"
+      "Content-Type: text/plain; charset=UTF-8\n"
+      "Content-Transfer-Encoding: 8bit\n"
+      "POT-Creation-Date: 2018-05-02T22:06:24+00:00\n"
+      "PO-Revision-Date: 2018-05-02T22:06:24+00:00\n"
+      "X-Domain: foo-plugin\n"
+      "Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+      #: foo-plugin.js:15
+      msgid "JS Only String"
+      msgstr "JS Only Translation"
+
+      #: foo-plugin.php:10
+      msgid "PHP String"
+      msgstr "PHP Translation"
+
+      #: foo-plugin.js:20
+      #: foo-plugin.php:15
+      msgid "Both JS and PHP"
+      msgstr "Both Translation"
+      """
+
+    When I run `wp i18n make-php foo-plugin`
+    Then STDOUT should contain:
+      """
+      Success: Created 1 file.
+      """
+    And the return code should be 0
+    And the foo-plugin/foo-plugin-de_DE.l10n.php file should exist
+    And the foo-plugin/foo-plugin-de_DE.l10n.php file should contain:
+      """
+      PHP Translation
+      """
+    And the foo-plugin/foo-plugin-de_DE.l10n.php file should contain:
+      """
+      Both Translation
+      """
+    And the foo-plugin/foo-plugin-de_DE.l10n.php file should not contain:
+      """
+      JS Only Translation
+      """
+
diff --git a/src/JsStringFilterTrait.php b/src/JsStringFilterTrait.php
new file mode 100644
index 00000000..c1ace362
--- /dev/null
+++ b/src/JsStringFilterTrait.php
@@ -0,0 +1,46 @@
+<?php
+
+namespace WP_CLI\I18n;
+
+use Gettext\Translation;
+use Gettext\Translations;
+
+trait JsStringFilterTrait {
+	/**
+	 * JavaScript file extensions to check for.
+	 *
+	 * @var string[]
+	 */
+	protected static $js_extensions = [ '.js', '.jsx', '.ts', '.tsx', '.mjs', '.cjs' ];
+
+	/**
+	 * Removes strings from translations that only occur in JavaScript files.
+	 *
+	 * @param Translations $translations The translations instance to filter.
+	 */
+	protected function remove_js_only_strings( Translations $translations ): void {
+		foreach ( $translations->getArrayCopy() as $translation ) {
+			/** @var Translation $translation */
+
+			if ( ! $translation->hasReferences() ) {
+				continue;
+			}
+
+			$has_non_js_reference = false;
+			foreach ( $translation->getReferences() as $reference ) {
+				$file      = $reference[0];
+				$extension = '.' . strtolower( pathinfo( $file, PATHINFO_EXTENSION ) );
+
+				if ( ! in_array( $extension, static::$js_extensions, true ) ) {
+					$has_non_js_reference = true;
+					break;
+				}
+			}
+
+			// If all references are JS files, remove this translation.
+			if ( ! $has_non_js_reference ) {
+				unset( $translations[ $translation->getId() ] );
+			}
+		}
+	}
+}
diff --git a/src/MakeJsonCommand.php b/src/MakeJsonCommand.php
index 2076ac57..b52c9a29 100644
--- a/src/MakeJsonCommand.php
+++ b/src/MakeJsonCommand.php
@@ -3,7 +3,6 @@
 namespace WP_CLI\I18n;
 
 use Gettext\Extractors\Po as PoExtractor;
-use Gettext\Generators\Po as PoGenerator;
 use Gettext\Translation;
 use Gettext\Translations;
 use WP_CLI;
@@ -44,13 +43,6 @@ class MakeJsonCommand extends WP_CLI_Command {
 	 * [--extensions=<extensions>]
 	 * : Additional custom JS extensions, comma separated list. By default searches for .min.js and .js extensions.
 	 *
-	 * [--purge]
-	 * : Whether to purge the strings that were extracted from the original source file. Defaults to true, use `--no-purge` to skip the removal.
-	 *
-	 * [--update-mo-files]
-	 * : Whether MO files should be updated as well after updating PO files.
-	 * Only has an effect when used in combination with `--purge`.
-	 *
 	 * [--pretty-print]
 	 * : Pretty-print resulting JSON files.
 	 *
@@ -63,8 +55,8 @@ class MakeJsonCommand extends WP_CLI_Command {
 	 *     # Create JSON files for all PO files in the languages directory
 	 *     $ wp i18n make-json languages
 	 *
-	 *     # Create JSON files for my-plugin-de_DE.po and leave the PO file untouched.
-	 *     $ wp i18n make-json my-plugin-de_DE.po /tmp --no-purge
+	 *     # Create JSON files for my-plugin-de_DE.po
+	 *     $ wp i18n make-json my-plugin-de_DE.po /tmp
 	 *
 	 *     # Create JSON files with mapping
 	 *     $ wp i18n make-json languages --use-map=build/map.json
@@ -80,12 +72,10 @@ class MakeJsonCommand extends WP_CLI_Command {
 	 * @throws WP_CLI\ExitException
 	 */
 	public function __invoke( $args, $assoc_args ) {
-		$assoc_args      = Utils\parse_shell_arrays( $assoc_args, array( 'use-map' ) );
-		$purge           = Utils\get_flag_value( $assoc_args, 'purge', true );
-		$update_mo_files = Utils\get_flag_value( $assoc_args, 'update-mo-files', true );
-		$map_paths       = Utils\get_flag_value( $assoc_args, 'use-map', false );
-		$domain          = Utils\get_flag_value( $assoc_args, 'domain', '' );
-		$extensions      = array_map(
+		$assoc_args = Utils\parse_shell_arrays( $assoc_args, array( 'use-map' ) );
+		$map_paths  = Utils\get_flag_value( $assoc_args, 'use-map', false );
+		$domain     = Utils\get_flag_value( $assoc_args, 'domain', '' );
+		$extensions = array_map(
 			function ( $extension ) {
 				return trim( $extension, ' .' );
 			},
@@ -130,25 +120,6 @@ function ( $extension ) {
 			if ( $file->isFile() && $file->isReadable() && 'po' === $file->getExtension() ) {
 				$result        = $this->make_json( $file->getRealPath(), $destination, $map, $domain, $extensions );
 				$result_count += count( $result );
-
-				if ( $purge ) {
-					$removed = $this->remove_js_strings_from_po_file( $file->getRealPath() );
-
-					if ( ! $removed ) {
-						WP_CLI::warning( sprintf( 'Could not update file %s', basename( $source ) ) );
-						continue;
-					}
-
-					if ( $update_mo_files ) {
-						$file_basename    = basename( $file->getFilename(), '.po' );
-						$destination_file = "{$destination}/{$file_basename}.mo";
-
-						$translations = Translations::fromPoFile( $file->getPathname() );
-						if ( ! $translations->toMoFile( $destination_file ) ) {
-							WP_CLI::warning( "Could not create file {$destination_file}" );
-						}
-					}
-				}
 			}
 		}
 
@@ -385,37 +356,4 @@ protected function build_json_files( $mapping, $base_file_name, $destination ) {
 
 		return $result;
 	}
-
-	/**
-	 * Removes strings from PO file that only occur in JavaScript file.
-	 *
-	 * @param string $source_file Path to the PO file.
-	 * @return bool True on success, false otherwise.
-	 */
-	protected function remove_js_strings_from_po_file( $source_file ) {
-		/** @var Translations[] $mapping */
-		$translations = new Translations();
-
-		PoExtractor::fromFile( $source_file, $translations );
-
-		foreach ( $translations->getArrayCopy() as $translation ) {
-			/** @var Translation $translation */
-
-			if ( ! $translation->hasReferences() ) {
-				continue;
-			}
-
-			foreach ( $translation->getReferences() as $reference ) {
-				$file = $reference[0];
-
-				if ( substr( $file, - 3 ) !== '.js' ) {
-					continue 2;
-				}
-			}
-
-			unset( $translations[ $translation->getId() ] );
-		}
-
-		return PoGenerator::toFile( $translations, $source_file );
-	}
 }
diff --git a/src/MakeMoCommand.php b/src/MakeMoCommand.php
index a13eeabc..89bc9865 100644
--- a/src/MakeMoCommand.php
+++ b/src/MakeMoCommand.php
@@ -3,6 +3,7 @@
 namespace WP_CLI\I18n;
 
 use DirectoryIterator;
+use Gettext\Translation;
 use Gettext\Translations;
 use IteratorIterator;
 use SplFileInfo;
@@ -11,6 +12,8 @@
 use WP_CLI_Command;
 
 class MakeMoCommand extends WP_CLI_Command {
+	use JsStringFilterTrait;
+
 	/**
 	 * Create MO files from PO files.
 	 *
@@ -88,6 +91,10 @@ public function __invoke( $args, $assoc_args ) {
 			$destination_file = "{$destination}/{$file_name}";
 
 			$translations = Translations::fromPoFile( $file->getPathname() );
+
+			// Remove JS-only strings from MO files to keep them small.
+			$this->remove_js_only_strings( $translations );
+
 			if ( ! $translations->toMoFile( $destination_file ) ) {
 				WP_CLI::warning( sprintf( 'Could not create file %s', $destination_file ) );
 				continue;
diff --git a/src/MakePhpCommand.php b/src/MakePhpCommand.php
index 1e7622e8..adecee2c 100644
--- a/src/MakePhpCommand.php
+++ b/src/MakePhpCommand.php
@@ -3,6 +3,7 @@
 namespace WP_CLI\I18n;
 
 use DirectoryIterator;
+use Gettext\Translation;
 use Gettext\Translations;
 use IteratorIterator;
 use SplFileInfo;
@@ -11,6 +12,8 @@
 use WP_CLI_Command;
 
 class MakePhpCommand extends WP_CLI_Command {
+	use JsStringFilterTrait;
+
 	/**
 	 * Create PHP files from PO files.
 	 *
@@ -82,7 +85,11 @@ public function __invoke( $args, $assoc_args ) {
 			$destination_file = "{$destination}/{$file_basename}.l10n.php";
 
 			$translations = Translations::fromPoFile( $file->getPathname() );
-			$options      = [ 'prettyPrint' => $pretty_print ];
+
+			// Remove JS-only strings from PHP files to keep them small.
+			$this->remove_js_only_strings( $translations );
+
+			$options = [ 'prettyPrint' => $pretty_print ];
 			if ( ! PhpArrayGenerator::toFile( $translations, $destination_file, $options ) ) {
 				WP_CLI::warning( sprintf( 'Could not create file %s', $destination_file ) );
 				continue;