diff --git a/web/inc/i18n.php b/web/inc/i18n.php
index 5e4f71c19..5971dc3d8 100644
--- a/web/inc/i18n.php
+++ b/web/inc/i18n.php
@@ -45,3 +45,68 @@ function __() {
     array_unshift($args,$_SESSION['language']);
     return call_user_func_array("_translate",$args);
 }
+
+/**
+ * Detects user language from Accept-Language HTTP header.
+ * @param string Fallback language (default: 'en')
+ * @return string Language code (such as 'en' and 'ja')
+ */
+function detect_user_language($fallback='en') {
+    static $user_lang = '';
+
+    // Already detected
+    if (!empty($user_lang)) return $user_lang;
+
+    // Check if Accept-Language header is available
+    if (!isset($_SERVER) ||
+        !isset($_SERVER['HTTP_ACCEPT_LANGUAGE']) ||
+        !is_string($_SERVER['HTTP_ACCEPT_LANGUAGE'])
+    ) {
+        // Store result for reusing
+        $user_lang = $fallback;
+        return $user_lang;
+    }
+
+    // Sort Accept-Language by `q` value
+    $accept_langs = explode(',', preg_replace('/\s/', '', strtolower($_SERVER['HTTP_ACCEPT_LANGUAGE'])));
+    $accept_langs_sorted = [];
+    foreach ($accept_langs as $lang) {
+        $div = explode(';q=', $lang, 2);
+        if (count($div) < 2) {
+            // `q` value was not specfied
+            // -> Set default `q` value (1)
+            $div[] = '1';
+        }
+        list($code, $q) = $div;
+        if (preg_match('/^[\w\-]+$/', $code)) {
+            // Acceptable language code
+            $accept_langs_sorted[$code] = (double)$q;
+        }
+    }
+    arsort($accept_langs_sorted);
+
+    // List lanugages
+    exec (VESTA_CMD."v-list-sys-languages json", $output, $return_var);
+    $languages = json_decode(implode('', $output), true);
+    unset($output);
+
+    // Find best matching language
+    foreach ($accept_langs_sorted as $user_lang => $dummy) {
+        $decision = '';
+        foreach ($languages as $prov_lang) {
+            if (strlen($decision) > strlen($prov_lang)) continue;
+            if (strpos($user_lang, $prov_lang) !== false) {
+                $decision = $prov_lang;
+            }
+        }
+        if (!empty($decision)) {
+            // Store result for reusing
+            $user_lang = $decision;
+            return $user_lang;
+        }
+    }
+
+    // Store result for reusing
+    $user_lang = $fallback;
+    return $user_lang;
+}
\ No newline at end of file
diff --git a/web/js/i18n.js.php b/web/js/i18n.js.php
index c3429d402..34f52f188 100644
--- a/web/js/i18n.js.php
+++ b/web/js/i18n.js.php
@@ -4,7 +4,7 @@ session_start();
 require_once($_SERVER['DOCUMENT_ROOT'].'/inc/i18n.php');
 
 if (empty($_SESSION['language'])) {
-    $_SESSION['language'] = 'en';
+    $_SESSION['language'] = detect_user_language();
 }
 ?>
 
diff --git a/web/login/index.php b/web/login/index.php
index 06617e2f4..f084ae174 100644
--- a/web/login/index.php
+++ b/web/login/index.php
@@ -93,8 +93,8 @@ foreach ($sys_arr as $key => $value) {
     $_SESSION[$key] = $value;
 }
 
-// Set default language
-if (empty($_SESSION['language'])) $_SESSION['language']='en';
+// Detect language
+if (empty($_SESSION['language'])) $_SESSION['language'] = detect_user_language();
 
 require_once($_SERVER['DOCUMENT_ROOT'].'/inc/i18n/'.$_SESSION['language'].'.php');
 require_once('../templates/header.html');
diff --git a/web/reset/index.php b/web/reset/index.php
index f84fb38da..abde3c145 100644
--- a/web/reset/index.php
+++ b/web/reset/index.php
@@ -74,14 +74,8 @@ if ((!empty($_POST['user'])) && (!empty($_POST['code'])) && (!empty($_POST['pass
     }
 }
 
-// Set system language
-exec (VESTA_CMD . "v-list-sys-config json", $output, $return_var);
-$data = json_decode(implode('', $output), true);
-if (!empty( $data['config']['LANGUAGE'])) {
-    $_SESSION['language'] = $data['config']['LANGUAGE'];
-} else {
-    $_SESSION['language'] = 'en';
-}
+// Detect language
+if (empty($_SESSION['language'])) $_SESSION['language'] = detect_user_language();
 
 if (empty($_GET['action'])) {
     require_once '../templates/header.html';
diff --git a/web/templates/admin/edit_user.html b/web/templates/admin/edit_user.html
index 894a8a2cc..8717ce3f6 100644
--- a/web/templates/admin/edit_user.html
+++ b/web/templates/admin/edit_user.html
@@ -125,7 +125,7 @@
                                                 if (( $value == $v_language ) || ( $svalue == $v_language)){
                                                     echo 'selected' ;
                                                 }
-                                                if (( $value == 'en' ) && (empty($v_language))){
+                                                if (( $value == detect_user_language() ) && (empty($v_language))){
                                                     echo 'selected' ;
                                                 }
                                                 echo ">".htmlentities($value)."</option>\n";
diff --git a/web/templates/user/edit_user.html b/web/templates/user/edit_user.html
index d42998a41..66600bd95 100644
--- a/web/templates/user/edit_user.html
+++ b/web/templates/user/edit_user.html
@@ -104,7 +104,7 @@
                                                 if (( $value == $v_language ) || ( $svalue == $v_language)){
                                                     echo 'selected' ;
                                                 }
-                                                if (( $value == 'en' ) && (empty($v_language))){
+                                                if (( $value == detect_user_language() ) && (empty($v_language))){
                                                     echo 'selected' ;
                                                 }
                                                 echo ">".htmlentities($value)."</option>\n";