Index: wp-testcase/test_includes_formatting.php
===================================================================
--- wp-testcase/test_includes_formatting.php	(revision 723)
+++ wp-testcase/test_includes_formatting.php	(working copy)
@@ -1082,6 +1082,11 @@
 		$this->assertEquals("6x7-is-42", sanitize_title_with_dashes("6×7 is 42", '', 'save'));
 	}
 
+	function test_replaces_standalone_diacritic() {
+		$this->knownWPBug(20772);
+		$this->assertEquals("aaaa", sanitize_title_with_dashes("āáǎà", '', 'save'));
+	}
+
 }
 
 class TestConvertChars extends WPTestCase {
@@ -1366,6 +1371,22 @@
 		// dot below 
 		$this->assertEquals( 'AaAaAaEeEeIiOoOoOoUuUuYy', remove_accents( 'ẠạẬậẶặẸẹỆệỊịỌọỘộỢợỤụỰựỴỵ' ) );
 	}
+
+	public function test_remove_accents_hanyu_pinyin() {
+		$this->knownWPBug(20772);
+
+		// Vowels with diacritic (Chinese, Hanyu Pinyin)
+		// macron
+		$this->assertEquals( 'aeiouuAEIOUU', remove_accents( 'āēīōūǖĀĒĪŌŪǕ' ) );
+		// acute accent
+		$this->assertEquals( 'aeiouuAEIOUU', remove_accents( 'áéíóúǘÁÉÍÓÚǗ' ) );
+		// caron
+		$this->assertEquals( 'aeiouuAEIOUU', remove_accents( 'ǎěǐǒǔǚǍĚǏǑǓǙ' ) );
+		// grave accent
+		$this->assertEquals( 'aeiouuAEIOUU', remove_accents( 'àèìòùǜÀÈÌÒÙǛ' ) );
+		// unmarked
+		$this->assertEquals( 'aaeiouuAEIOUU', remove_accents( 'aɑeiouüAEIOUÜ' ) );
+	}
 }
 
 class TestStripSlashesDeep extends WPTestCase {