diff --git a/composer.json b/composer.json
index edb9138d79..5e2bb13b13 100644
--- a/composer.json
+++ b/composer.json
@@ -33,7 +33,6 @@
     ],
     "require": {
         "php": ">=5.5.0",
-        "ext-mbstring": "*",
         "ext-mysqli": "*",
         "ext-xml": "*",
         "ext-pcre": "*",
@@ -46,7 +45,8 @@
         "psr/container": "^1.0",
         "twig/twig": "^1.32",
         "twig/extensions": "~1.4.1",
-        "symfony/expression-language": "^3.2"
+        "symfony/expression-language": "^3.2",
+        "symfony/polyfill-mbstring": "^1.3"
     },
     "conflict": {
         "tecnickcom/tcpdf": "<6.2"
@@ -59,6 +59,7 @@
         "ext-bz2": "For bzip2 import and export",
         "ext-zip": "For zip import and export",
         "ext-gd2": "For image transformations",
+        "ext-mbstring": "For best performance",
         "tecnickcom/tcpdf": "For PDF support"
     },
     "require-dev": {
diff --git a/doc/require.rst b/doc/require.rst
index a6e84ebc39..0de03a5728 100644
--- a/doc/require.rst
+++ b/doc/require.rst
@@ -13,7 +13,10 @@ PHP
 ---
 
 * You need PHP 5.5.0 or newer, with ``session`` support, the Standard PHP Library
-  (SPL) extension, JSON support, and the ``mbstring`` extension (see :term:`mbstring`).
+  (SPL) extension, and JSON support.
+
+* The ``mbstring`` extension (see :term:`mbstring`) is strongly recommended
+  for performance reasons.
 
 * To support uploading of ZIP files, you need the PHP ``zip`` extension.
 
diff --git a/libraries/Encoding.php b/libraries/Encoding.php
index 1f58bb61b3..209d94f406 100644
--- a/libraries/Encoding.php
+++ b/libraries/Encoding.php
@@ -195,10 +195,7 @@ class Encoding
      */
     public static function canConvertKanji()
     {
-        return (
-            $GLOBALS['lang'] == 'ja' &&
-            function_exists('mb_convert_encoding')
-        );
+        return $GLOBALS['lang'] == 'ja';
     }
 
     /**
diff --git a/libraries/config/FormDisplay.php b/libraries/config/FormDisplay.php
index 86b71e7415..1dbd458756 100644
--- a/libraries/config/FormDisplay.php
+++ b/libraries/config/FormDisplay.php
@@ -818,13 +818,7 @@ class FormDisplay
                     'recode', 'recode'
                 );
             }
-            if (!function_exists('mb_convert_encoding')) {
-                $opts['values']['mb'] .= ' (' . __('unavailable') . ')';
-                $comment .= ($comment ? ", " : '') . sprintf(
-                    __('"%s" requires %s extension'),
-                    'mb', 'mbstring'
-                );
-            }
+            /* mbstring is always there thanks to polyfill */
             $opts['comment'] = $comment;
             $opts['comment_warning'] = true;
         }
diff --git a/libraries/core.lib.php b/libraries/core.lib.php
index 436ae46a60..5fea4b4d5f 100644
--- a/libraries/core.lib.php
+++ b/libraries/core.lib.php
@@ -17,11 +17,6 @@ if (! defined('PHPMYADMIN')) {
     exit;
 }
 
-/**
- * String handling (security)
- */
-require_once 'libraries/string.lib.php';
-
 /**
  * checks given $var and returns it if valid, or $default of not valid
  * given $var is also checked for type being 'similar' as $default
@@ -235,15 +230,7 @@ function PMA_fatalError($error_message, $message_args = null) {
         $response->addJSON('message', PMA\libraries\Message::error($error_message));
     } else {
         $error_message = strtr($error_message, array('<br />' => '[br]'));
-
-        // these variables are used in the included file libraries/error.inc.php
-        //first check if php-mbstring is available
-        if (function_exists('mb_detect_encoding')) {
-            //If present use gettext
-            $error_header = __('Error');
-        } else {
-            $error_header = 'Error';
-        }
+        $error_header = __('Error');
         $lang = isset($GLOBALS['lang']) ? $GLOBALS['lang'] : 'en';
         $dir = isset($GLOBALS['text_dir']) ? $GLOBALS['text_dir'] : 'ltr';
 
@@ -916,7 +903,7 @@ function PMA_checkExtensions()
      * Warning about mbstring.
      */
     if (! function_exists('mb_detect_encoding')) {
-        PMA_warnMissingExtension('mbstring', true);
+        PMA_warnMissingExtension('mbstring');
     }
 
     /**
diff --git a/libraries/string.lib.php b/libraries/string.lib.php
deleted file mode 100644
index e1e54f37d3..0000000000
--- a/libraries/string.lib.php
+++ /dev/null
@@ -1,33 +0,0 @@
-<?php
-/* vim: set expandtab sw=4 ts=4 sts=4: */
-/** String Functions for phpMyAdmin
- *
- * If mb_* functions don't exist, we create the ones we need and they'll use the
- * standard string functions.
- *
- * All mb_* functions created by PMA should behave as mb_* functions.
- *
- * @package PhpMyAdmin
- */
-if (! defined('PHPMYADMIN')) {
-    exit;
-}
-
-if (!defined('MULTIBYTES_ON')) {
-    define('MULTIBYTES_ON', true);
-    define('MULTIBYTES_OFF', false);
-}
-
-if (@function_exists('mb_strlen')) {
-    if (!defined('MULTIBYTES_STATUS')) {
-        define('MULTIBYTES_STATUS', MULTIBYTES_ON);
-    }
-
-    include_once 'libraries/stringMb.lib.php';
-} else {
-    if (!defined('MULTIBYTES_STATUS')) {
-        define('MULTIBYTES_STATUS', MULTIBYTES_OFF);
-    }
-
-    include_once 'libraries/stringNative.lib.php';
-}
diff --git a/libraries/stringMb.lib.php b/libraries/stringMb.lib.php
deleted file mode 100644
index 9c8d5f64f1..0000000000
--- a/libraries/stringMb.lib.php
+++ /dev/null
@@ -1,76 +0,0 @@
-<?php
-/* vim: set expandtab sw=4 ts=4 sts=4: */
-/** String Functions for phpMyAdmin
- *
- * If mb_* functions don't exist, we create the ones we need and they'll use the
- * standard string functions.
- *
- * All mb_* functions created by PMA should behave as mb_* functions.
- *
- * @package PhpMyAdmin
- */
-if (! defined('PHPMYADMIN')) {
-    exit;
-}
-
-if (!@function_exists('mb_ord')) {
-    /**
-     * Perform a regular expression match
-     *
-     * Take care: might not work with lookbehind expressions.
-     *
-     * @param string $pattern Pattern to search for
-     * @param string $subject Input string
-     * @param int    $offset  Start from search
-     *
-     * @return int 1 if matched, 0 if doesn't, false on failure
-     */
-    function mb_preg_strpos($pattern, $subject, $offset = 0)
-    {
-        $matches = array();
-        $bFind = preg_match(
-            $pattern, mb_substr($subject, $offset), $matches, PREG_OFFSET_CAPTURE
-        );
-        if (1 !== $bFind) {
-            return false;
-        }
-
-        return $matches[1][1] + $offset;
-    }
-
-    /**
-     * Get the ordinal value of a string
-     *
-     * @param string $string the string for which ord is required
-     *
-     * @return int the ord value
-     */
-    function mb_ord($string)
-    {
-        if (false === $string || null === $string || '' === $string) {
-            return 0;
-        }
-
-        $str = mb_convert_encoding($string, "UCS-4BE", "UTF-8");
-        $substr = mb_substr($str, 0, 1, "UCS-4BE");
-        $val = unpack("N", $substr);
-        return $val[1];
-    }
-
-    /**
-     * Get the character of an ASCII
-     *
-     * @param int $ascii the ASCII code for which character is required
-     *
-     * @return string the character
-     */
-    function mb_chr($ascii)
-    {
-        return mb_convert_encoding(
-            pack("N", $ascii),
-            'utf-8',
-            'UCS-4BE'
-        );
-    }
-
-}
diff --git a/libraries/stringNative.lib.php b/libraries/stringNative.lib.php
deleted file mode 100644
index 557a02f8cb..0000000000
--- a/libraries/stringNative.lib.php
+++ /dev/null
@@ -1,245 +0,0 @@
-<?php
-/* vim: set expandtab sw=4 ts=4 sts=4: */
-/** String Functions for phpMyAdmin
- * If mb_* functions don't exist, we create the ones we need and they'll use the
- * standard string functions.
- * All mb_* functions created by PMA should behave as mb_* functions.
- *
- * @package PhpMyAdmin
- */
-if (!defined('PHPMYADMIN')) {
-    exit;
-}
-
-//Define mb_* functions if they don't exist.
-if (!@function_exists('mb_strlen')) {
-    /**
-     * Returns length of string depending on current charset.
-     *
-     * @param string $string string to count
-     *
-     * @return int string length
-     */
-    function mb_strlen($string)
-    {
-        return strlen($string);
-    }
-
-    /**
-     * Returns substring from string, works depending on current charset.
-     *
-     * @param string $string string to count
-     * @param int    $start  start of substring
-     * @param int    $length length of substring
-     *
-     * @return string the sub string
-     */
-    function mb_substr($string, $start, $length = 2147483647)
-    {
-        if (null === $string || strlen($string) <= $start) {
-            return '';
-        }
-        if (null === $length) {
-            $length = 2147483647;
-        }
-        return substr($string, $start, $length);
-    }
-
-    /**
-     * Returns number of substring from string.
-     *
-     * @param string $string string to check
-     * @param int    $needle string to count
-     *
-     * @return int number of substring from the string
-     */
-    function mb_substrCount($string, $needle)
-    {
-        return substr_count($string, $needle);
-    }
-
-    /**
-     * Returns position of $needle in $haystack or false if not found
-     *
-     * @param string $haystack the string being checked
-     * @param string $needle   the string to find in haystack
-     * @param int    $offset   the search offset
-     *
-     * @return integer position of $needle in $haystack or false
-     */
-    function mb_strpos($haystack, $needle, $offset = 0)
-    {
-        return strpos($haystack, $needle, $offset);
-    }
-
-    /**
-     * Returns position of $needle in $haystack - case insensitive - or false if
-     * not found
-     *
-     * @param string $haystack the string being checked
-     * @param string $needle   the string to find in haystack
-     * @param int    $offset   the search offset
-     *
-     * @return integer position of $needle in $haystack or false
-     */
-    function mb_stripos($haystack, $needle, $offset = 0)
-    {
-        if (('' === $haystack || false === $haystack) && $offset >= strlen($haystack)
-        ) {
-            return false;
-        }
-        return stripos($haystack, $needle, $offset);
-    }
-
-    /**
-     * Returns position of last $needle in $haystack or false if not found
-     *
-     * @param string $haystack the string being checked
-     * @param string $needle   the string to find in haystack
-     * @param int    $offset   the search offset
-     *
-     * @return integer position of last $needle in $haystack or false
-     */
-    function mb_strrpos($haystack, $needle, $offset = 0)
-    {
-        return strrpos($haystack, $needle, $offset);
-    }
-
-    /**
-     * Returns position of last $needle in $haystack - case insensitive - or false
-     * if not found
-     *
-     * @param string $haystack the string being checked
-     * @param string $needle   the string to find in haystack
-     * @param int    $offset   the search offset
-     *
-     * @return integer position of last $needle in $haystack or false
-     */
-    function mb_strripos($haystack, $needle, $offset = 0)
-    {
-        if (('' === $haystack || false === $haystack) && $offset >= strlen($haystack)
-        ) {
-            return false;
-        }
-        return strripos($haystack, $needle, $offset);
-    }
-
-    /**
-     * Returns part of $haystack string starting from and including the first
-     * occurrence of $needle to the end of $haystack or false if not found
-     *
-     * @param string $haystack      the string being checked
-     * @param string $needle        the string to find in haystack
-     * @param bool   $before_needle the part before the needle
-     *
-     * @return string part of $haystack or false
-     */
-    function mb_strstr($haystack, $needle, $before_needle = false)
-    {
-        return strstr($haystack, $needle, $before_needle);
-    }
-
-    /**
-     * Returns part of $haystack string starting from and including the first
-     * occurrence of $needle to the end of $haystack - case insensitive - or false
-     * if not found
-     *
-     * @param string $haystack      the string being checked
-     * @param string $needle        the string to find in haystack
-     * @param bool   $before_needle the part before the needle
-     *
-     * @return string part of $haystack or false
-     */
-    function mb_stristr($haystack, $needle, $before_needle = false)
-    {
-        return stristr($haystack, $needle, $before_needle);
-    }
-
-    /**
-     * Returns the portion of haystack which starts at the last occurrence or false
-     * if not found
-     *
-     * @param string $haystack the string being checked
-     * @param string $needle   the string to find in haystack
-     *
-     * @return string portion of haystack which starts at the last occurrence or
-     *                         false
-     */
-    function mb_strrchr($haystack, $needle)
-    {
-        return strrchr($haystack, $needle);
-    }
-
-    /**
-     * Make a string lowercase
-     *
-     * @param string $string the string being lowercased
-     *
-     * @return string the lower case string
-     */
-    function mb_strtolower($string)
-    {
-        return strtolower($string);
-    }
-
-    /**
-     * Make a string uppercase
-     *
-     * @param string $string the string being uppercased
-     *
-     * @return string the upper case string
-     */
-    function mb_strtoupper($string)
-    {
-        return strtoupper($string);
-    }
-}
-
-//New functions.
-if (!@function_exists('mb_ord')) {
-    /**
-     * Perform a regular expression match
-     *
-     * @param string $pattern Pattern to search for
-     * @param string $subject Input string
-     * @param int    $offset  Start from search
-     *
-     * @return int 1 if matched, 0 if doesn't, false on failure
-     */
-    function mb_preg_strpos($pattern, $subject, $offset = 0)
-    {
-        $matches = array();
-        $bFind = preg_match(
-            $pattern, $subject, $matches, PREG_OFFSET_CAPTURE, $offset
-        );
-        if (1 !== $bFind) {
-            return false;
-        }
-
-        return $matches[1][1];
-    }
-
-    /**
-     * Get the ordinal value of a string
-     *
-     * @param string $string the string for which ord is required
-     *
-     * @return int the ord value
-     */
-    function mb_ord($string)
-    {
-        return ord($string);
-    }
-
-    /**
-     * Get the character of an ASCII
-     *
-     * @param int $ascii the ASCII code for which character is required
-     *
-     * @return string the character
-     */
-    function mb_chr($ascii)
-    {
-        return chr($ascii);
-    }
-}
\ No newline at end of file
diff --git a/test/classes/DisplayResultsTest.php b/test/classes/DisplayResultsTest.php
index 63387cf3a8..e561734f7a 100644
--- a/test/classes/DisplayResultsTest.php
+++ b/test/classes/DisplayResultsTest.php
@@ -11,7 +11,6 @@
 use PMA\libraries\plugins\transformations\Text_Plain_Link;
 
 require_once 'libraries/relation.lib.php';
-require_once 'libraries/string.lib.php';
 require_once 'test/PMATestCase.php';
 
 /**
diff --git a/test/classes/EncodingTest.php b/test/classes/EncodingTest.php
index 01a5c54f8d..d1d145c566 100644
--- a/test/classes/EncodingTest.php
+++ b/test/classes/EncodingTest.php
@@ -84,10 +84,6 @@ class EncodingTest extends PHPUnit_Framework_TestCase
 
     public function testMbstring()
     {
-        if (! @function_exists('mb_convert_encoding')) {
-            $this->markTestSkipped('mbstring extension missing');
-        }
-
         Encoding::setEngine(Encoding::ENGINE_MB);
         $this->assertEquals(
             "This is the Euro symbol '?'.",
diff --git a/test/classes/config/FormDisplayTest.php b/test/classes/config/FormDisplayTest.php
index 9fe2940a50..96a703e421 100644
--- a/test/classes/config/FormDisplayTest.php
+++ b/test/classes/config/FormDisplayTest.php
@@ -411,6 +411,7 @@ class FormDisplayTest extends PMATestCase
         $opts = array('values' => array());
         $opts['values']['iconv'] = 'testIconv';
         $opts['values']['recode'] = 'testRecode';
+        $opts['values']['mb'] = 'testMB';
 
         $expect = $opts;