diff --git a/lib/compat/wordpress-6.5/fonts/class-wp-font-collection.php b/lib/compat/wordpress-6.5/fonts/class-wp-font-collection.php
index 019cf0f3f0b29..31bb410eb4d86 100644
--- a/lib/compat/wordpress-6.5/fonts/class-wp-font-collection.php
+++ b/lib/compat/wordpress-6.5/fonts/class-wp-font-collection.php
@@ -48,10 +48,10 @@ final class WP_Font_Collection {
 		 *
 		 * @since 6.5.0
 		 *
-		 * @param string        $slug         Font collection slug.
-		 * @param array|string  $data_or_file Font collection data array or a path/URL to a JSON file
-		 *                                    containing the font collection.
-		 *                                    See {@see wp_register_font_collection()} for the supported fields.
+		 * @param string       $slug         Font collection slug.
+		 * @param array|string $data_or_file Font collection data array or a path/URL to a JSON file
+		 *                                   containing the font collection.
+		 *                                   See {@see wp_register_font_collection()} for the supported fields.
 		 */
 		public function __construct( $slug, $data_or_file ) {
 			$this->slug = sanitize_title( $slug );
@@ -162,7 +162,7 @@ private function load_from_url( $url ) {
 
 				$data = json_decode( wp_remote_retrieve_body( $response ), true );
 				if ( empty( $data ) ) {
-					return new WP_Error( 'font_collection_decode_error', __( 'Error decoding the font collection data from the REST response JSON.', 'gutenberg' ) );
+					return new WP_Error( 'font_collection_decode_error', __( 'Error decoding the font collection data from the HTTP response JSON.', 'gutenberg' ) );
 				}
 
 				// Make sure the data is valid before storing it in a transient.
@@ -193,8 +193,8 @@ private function sanitize_and_validate_data( $data ) {
 			foreach ( $required_properties as $property ) {
 				if ( empty( $data[ $property ] ) ) {
 					$message = sprintf(
-					// translators: 1: Font collection slug, 2: Missing property name.
-						__( 'Font collection "%1$s" has missing or empty property: "%2$s."', 'gutenberg' ),
+					// translators: 1: Font collection slug, 2: Missing property name, e.g. "font_families".
+						__( 'Font collection "%1$s" has missing or empty property: "%2$s".', 'gutenberg' ),
 						$this->slug,
 						$property
 					);
diff --git a/lib/compat/wordpress-6.5/fonts/class-wp-font-library.php b/lib/compat/wordpress-6.5/fonts/class-wp-font-library.php
index 9bf90ca1d9dd8..ce0841015b39c 100644
--- a/lib/compat/wordpress-6.5/fonts/class-wp-font-library.php
+++ b/lib/compat/wordpress-6.5/fonts/class-wp-font-library.php
@@ -125,7 +125,7 @@ public function get_font_collection( $slug ) {
 			if ( array_key_exists( $slug, $this->collections ) ) {
 				return $this->collections[ $slug ];
 			}
-			return new WP_Error( 'font_collection_not_found', 'Font collection not found.' );
+			return new WP_Error( 'font_collection_not_found', __( 'Font collection not found.', 'gutenberg' ) );
 		}
 
 		/**
diff --git a/lib/compat/wordpress-6.5/fonts/class-wp-font-utils.php b/lib/compat/wordpress-6.5/fonts/class-wp-font-utils.php
index b75ce0ec41cf6..23c95d633fb47 100644
--- a/lib/compat/wordpress-6.5/fonts/class-wp-font-utils.php
+++ b/lib/compat/wordpress-6.5/fonts/class-wp-font-utils.php
@@ -44,7 +44,7 @@ public static function sanitize_font_family( $font_family ) {
 			$wrapped_font_families = array_map(
 				function ( $family ) {
 					$trimmed = trim( $family );
-					if ( ! empty( $trimmed ) && false !== strpos( $trimmed, ' ' ) && false === strpos( $trimmed, "'" ) && false === strpos( $trimmed, '"' ) ) {
+					if ( ! empty( $trimmed ) && str_contains( $trimmed, ' ' ) && ! str_contains( $trimmed, "'" ) && ! str_contains( $trimmed, '"' ) ) {
 							return '"' . $trimmed . '"';
 					}
 					return $trimmed;
@@ -215,13 +215,17 @@ private static function apply_sanitizer( $value, $sanitizer ) {
 		}
 
 		/**
-		 * Provide the expected mime-type value for font files per-PHP release. Due to differences in the values returned these values differ between PHP versions.
+		 * Returns the expected mime-type values for font files, depending on PHP version.
 		 *
-		 * This is necessary until a collection of valid mime-types per-file extension can be provided to 'upload_mimes' filter.
+		 * This is needed because font mime types vary by PHP version, so checking the PHP version
+		 * is necessary until a list of valid mime-types for each file extension can be provided to
+		 * the 'upload_mimes' filter.
 		 *
 		 * @since 6.5.0
 		 *
-		 * @return Array A collection of mime types keyed by file extension.
+		 * @access private
+		 *
+		 * @return array A collection of mime types keyed by file extension.
 		 */
 		public static function get_allowed_font_mime_types() {
 			$php_7_ttf_mime_type = PHP_VERSION_ID >= 70300 ? 'application/font-sfnt' : 'application/x-font-ttf';
diff --git a/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-collections-controller.php b/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-collections-controller.php
index 06a073d426abc..90ee80649bb48 100644
--- a/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-collections-controller.php
+++ b/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-collections-controller.php
@@ -319,7 +319,7 @@ public function get_items_permissions_check( $request ) { // phpcs:ignore Variab
 
 			return new WP_Error(
 				'rest_cannot_read',
-				__( 'Sorry, you are not allowed to use the Font Library on this site.', 'gutenberg' ),
+				__( 'Sorry, you are not allowed to access font collections.', 'gutenberg' ),
 				array(
 					'status' => rest_authorization_required_code(),
 				)
diff --git a/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-faces-controller.php b/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-faces-controller.php
index 60f04e9ff23df..0ecd069fc230c 100644
--- a/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-faces-controller.php
+++ b/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-faces-controller.php
@@ -180,8 +180,8 @@ public function validate_create_font_face_settings( $value, $request ) {
 				if ( isset( $settings[ $key ] ) && ! $settings[ $key ] ) {
 					return new WP_Error(
 						'rest_invalid_param',
-						/* translators: %s: Font family setting key. */
-						sprintf( __( 'font_face_setting[%s] cannot be empty.', 'gutenberg' ), $key ),
+						/* translators: %s: Name of the missing font face settings parameter, e.g. "font_face_settings[src]". */
+						sprintf( __( '%s cannot be empty.', 'gutenberg' ), "font_face_setting[ $key ]" ),
 						array( 'status' => 400 )
 					);
 				}
@@ -196,7 +196,8 @@ public function validate_create_font_face_settings( $value, $request ) {
 				if ( empty( $src ) ) {
 					return new WP_Error(
 						'rest_invalid_param',
-						__( 'font_face_settings[src] values must be non-empty strings.', 'gutenberg' ),
+						/* translators: %s: Font face source parameter name: "font_face_settings[src]". */
+						sprintf( __( '%s values must be non-empty strings.', 'gutenberg' ), 'font_face_settings[src]' ),
 						array( 'status' => 400 )
 					);
 				}
@@ -205,8 +206,8 @@ public function validate_create_font_face_settings( $value, $request ) {
 				if ( false === wp_http_validate_url( $src ) && ! isset( $files[ $src ] ) ) {
 					return new WP_Error(
 						'rest_invalid_param',
-						/* translators: %s: src value in the font face settings. */
-						sprintf( __( 'font_face_settings[src] value "%s" must be a valid URL or file reference.', 'gutenberg' ), $src ),
+						/* translators: 1: Font face source parameter name: "font_face_settings[src]", 2: The invalid src value. */
+						sprintf( __( '%1$s value "%2$s" must be a valid URL or file reference.', 'gutenberg' ), 'font_face_settings[src]', $src ),
 						array( 'status' => 400 )
 					);
 				}
@@ -217,8 +218,8 @@ public function validate_create_font_face_settings( $value, $request ) {
 				if ( ! in_array( $file, $srcs, true ) ) {
 					return new WP_Error(
 						'rest_invalid_param',
-						// translators: %s: File key (e.g. `file-0`) in the request data.
-						sprintf( __( 'File %1$s must be used in font_face_settings[src].', 'gutenberg' ), $file ),
+						/* translators: 1: File key (e.g. "file-0") in the request data, 2: Font face source parameter name: "font_face_settings[src]". */
+						sprintf( __( 'File %1$s must be used in %2$s.', 'gutenberg' ), $file, 'font_face_settings[src]' ),
 						array( 'status' => 400 )
 					);
 				}
@@ -291,7 +292,7 @@ public function get_item( $request ) {
 				return new WP_Error(
 					'rest_font_face_parent_id_mismatch',
 					/* translators: %d: A post id. */
-					sprintf( __( 'The font face does not belong to the specified font family with id of "%d"', 'gutenberg' ), $font_family->ID ),
+					sprintf( __( 'The font face does not belong to the specified font family with id of "%d".', 'gutenberg' ), $font_family->ID ),
 					array( 'status' => 404 )
 				);
 			}
@@ -405,7 +406,7 @@ public function delete_item( $request ) {
 				return new WP_Error(
 					'rest_font_face_parent_id_mismatch',
 					/* translators: %d: A post id. */
-					sprintf( __( 'The font face does not belong to the specified font family with id of "%d"', 'gutenberg' ), $font_family->ID ),
+					sprintf( __( 'The font face does not belong to the specified font family with id of "%d".', 'gutenberg' ), $font_family->ID ),
 					array( 'status' => 404 )
 				);
 			}
diff --git a/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-families-controller.php b/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-families-controller.php
index e4a2b2f8e9781..dbd59abd6085a 100644
--- a/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-families-controller.php
+++ b/lib/compat/wordpress-6.5/fonts/class-wp-rest-font-families-controller.php
@@ -86,7 +86,8 @@ public function validate_font_family_settings( $value, $request ) {
 			if ( null === $settings ) {
 				return new WP_Error(
 					'rest_invalid_param',
-					__( 'font_family_settings parameter must be a valid JSON string.', 'gutenberg' ),
+					/* translators: %s: Parameter name: "font_family_settings". */
+					sprintf( __( '%s parameter must be a valid JSON string.', 'gutenberg' ), 'font_family_settings' ),
 					array( 'status' => 400 )
 				);
 			}
@@ -102,7 +103,8 @@ public function validate_font_family_settings( $value, $request ) {
 				if ( isset( $settings['slug'] ) ) {
 					return new WP_Error(
 						'rest_invalid_param',
-						__( 'font_family_settings[slug] cannot be updated.', 'gutenberg' ),
+						/* translators: %s: Name of parameter being updated: font_family_settings[slug]". */
+						sprintf( __( '%s cannot be updated.', 'gutenberg' ), 'font_family_settings[slug]' ),
 						array( 'status' => 400 )
 					);
 				}
@@ -121,8 +123,8 @@ public function validate_font_family_settings( $value, $request ) {
 				if ( isset( $settings[ $key ] ) && ! $settings[ $key ] ) {
 					return new WP_Error(
 						'rest_invalid_param',
-						/* translators: %s: Font family setting key. */
-						sprintf( __( 'font_family_settings[%s] cannot be empty.', 'gutenberg' ), $key ),
+						/* translators: %s: Name of the empty font family setting parameter, e.g. "font_family_settings[slug]". */
+						sprintf( __( '%s cannot be empty.', 'gutenberg' ), "font_family_settings[ $key ]" ),
 						array( 'status' => 400 )
 					);
 				}
diff --git a/phpunit/tests/fonts/font-library/wpRestFontFacesController.php b/phpunit/tests/fonts/font-library/wpRestFontFacesController.php
index 273862e3047e8..042928c73da3f 100644
--- a/phpunit/tests/fonts/font-library/wpRestFontFacesController.php
+++ b/phpunit/tests/fonts/font-library/wpRestFontFacesController.php
@@ -350,7 +350,7 @@ public function test_get_item_invalid_parent_id() {
 		$response = rest_get_server()->dispatch( $request );
 		$this->assertErrorResponse( 'rest_font_face_parent_id_mismatch', $response, 404 );
 
-		$expected_message = 'The font face does not belong to the specified font family with id of "' . self::$other_font_family_id . '"';
+		$expected_message = 'The font face does not belong to the specified font family with id of "' . self::$other_font_family_id . '".';
 		$this->assertSame( $expected_message, $response->as_error()->get_error_messages()[0], 'The message must contain the correct parent ID.' );
 	}
 
@@ -928,7 +928,7 @@ public function test_delete_item_invalid_parent_id() {
 		$response = rest_get_server()->dispatch( $request );
 		$this->assertErrorResponse( 'rest_font_face_parent_id_mismatch', $response, 404, 'The response should return an error for "rest_font_face_parent_id_mismatch" with 404 status.' );
 
-		$expected_message = 'The font face does not belong to the specified font family with id of "' . self::$other_font_family_id . '"';
+		$expected_message = 'The font face does not belong to the specified font family with id of "' . self::$other_font_family_id . '".';
 		$this->assertSame( $expected_message, $response->as_error()->get_error_messages()[0], 'The message must contain the correct parent ID.' );
 	}