diff --git a/core/lib/Drupal/Component/Transliteration/PhpTransliteration.php b/core/lib/Drupal/Component/Transliteration/PhpTransliteration.php
index 3cd8d6856500ba50ca7e44317d110c41b0c33f55..5eee57aa200cc627f10104f59944712a3b71af1b 100644
--- a/core/lib/Drupal/Component/Transliteration/PhpTransliteration.php
+++ b/core/lib/Drupal/Component/Transliteration/PhpTransliteration.php
@@ -105,31 +105,55 @@ public function removeDiacritics($string) {
    * {@inheritdoc}
    */
   public function transliterate($string, $langcode = 'en', $unknown_character = '?', $max_length = NULL) {
-    $result = '';
+    $results = [];
     $length = 0;
-    // Split into Unicode characters and transliterate each one.
-    foreach (preg_split('//u', $string, 0, PREG_SPLIT_NO_EMPTY) as $character) {
-      $code = self::ordUTF8($character);
-      if ($code == -1) {
-        $to_add = $unknown_character;
-      }
-      else {
-        $to_add = $this->replace($code, $langcode, $unknown_character);
-      }
 
-      // Check if this exceeds the maximum allowed length.
-      if (isset($max_length)) {
-        $length += strlen($to_add);
-        if ($length > $max_length) {
-          // There is no more space.
-          return $result;
+    // Split on words to handle mixed case per word.
+    $words = explode(' ', $string);
+    foreach ($words as $key => $word) {
+      $results[$key] = '';
+
+      // String is mixed case if it consists of both uppercase and lowercase
+      // letters. To accurately check this, remove any numbers and check that
+      // remaining characters are not all uppercase and not all lowercase.
+      $alpha_string = preg_replace('/\\d/', '', $word);
+      $mixed_case = (strlen($alpha_string) > 1 && mb_strtolower($alpha_string) !== $alpha_string && mb_strtoupper($alpha_string) !== $alpha_string);
+
+      // Split into Unicode characters and transliterate each one.
+      foreach (preg_split('//u', $word, 0, PREG_SPLIT_NO_EMPTY) as $character) {
+        $code = self::ordUTF8($character);
+        if ($code == -1) {
+          $to_add = $unknown_character;
         }
+        else {
+          $to_add = $this->replace($code, $langcode, $unknown_character);
+        }
+
+        // Check if this exceeds the maximum allowed length.
+        if (isset($max_length)) {
+          $length += strlen($to_add);
+          if ($length > $max_length) {
+            // There is no more space.
+            $results = array_filter($results);
+            return implode(' ', $results);
+          }
+        }
+
+        // If this is a capitalised letter of a mixed case word, only capitalise
+        // the first letter and lowercase any subsequent letters.
+        if ($mixed_case && strlen($to_add) > 1 && mb_strtoupper($to_add) === $to_add) {
+          $to_add = ucfirst(strtolower($to_add));
+        }
+
+        $results[$key] .= $to_add;
       }
 
-      $result .= $to_add;
+      // Add space to count for max length.
+      $length++;
     }
 
-    return $result;
+    $results = array_filter($results);
+    return implode(' ', $results);
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Component/Transliteration/PhpTransliterationTest.php b/core/tests/Drupal/Tests/Component/Transliteration/PhpTransliterationTest.php
index 924f3e93000b8799b7054da9574578f052cf0604..eb468c8b80309484bb28680dbaf9ae76f975074c 100644
--- a/core/tests/Drupal/Tests/Component/Transliteration/PhpTransliterationTest.php
+++ b/core/tests/Drupal/Tests/Component/Transliteration/PhpTransliterationTest.php
@@ -146,6 +146,19 @@ public function providerTestPhpTransliteration() {
       ['en', chr(0xF8) . chr(0x80) . chr(0x80) . chr(0x80) . chr(0x80), '?'],
       // Max length.
       ['de', $two_byte, 'Ae Oe', '?', 5],
+      // Test strings with mixed case words where a single capital character
+      // results in multiple characters. The first character should remain
+      // capitalised but subsequent resulting characters should be lowercase.
+      // For example a result of the transliteration should be 'Shtrikhkod'
+      // not 'SHtrikhkod'. Numbers should not be used in determining whether a
+      // string is mixed case.
+      ['ru', 'Штрихкод', 'Shtrikhkod'],
+      ['bg', 'Щастие', 'Schastie'],
+      ['bg', 'Щ1', 'SCH1'],
+      ['bg', 'Щ1Щ', 'SCH1SCH'],
+      ['bg', 'Щ1щ', 'Sch1sch'],
+      ['bg', 'Щастие ЩЩЩ', 'Schastie SCHSCHSCH'],
+      ['bg', 'Щастие ЩЩЩ. Щастие! Щастие', 'Schastie SCHSCHSCH. Schastie! Schastie'],
     ];
   }