diff --git a/js/admin.js b/js/admin.js
index faaec1d..0153ec0 100644
--- a/js/admin.js
+++ b/js/admin.js
@@ -30,11 +30,11 @@ function editUser() {
   var userForm = document.getElementsByName('user')[0];
   var userLogin = userForm.options[userForm.selectedIndex].text;
   if (userLogin == auth) {
-    alert('Your can\'t edit your own user with this tool');
+    alert(lang['selfeditwarn']);
     return;
   }
-  var message = '<div style="float:left">You are editing user <b>' + userLogin + '</b></div>';
-  message += '<div class="red-button"><b><a href="javascript:void(0);" onclick="submitUser(\'delete\'); return false">Delete user</a></b></div>';
+  var message = '<div style="float:left">' + sprintf(lang['editinguser'], '<b>' + userLogin + '</b>') + '</div>';
+  message += '<div class="red-button"><b><a href="javascript:void(0);" onclick="submitUser(\'delete\'); return false">' + lang['deluser'] + '</a></b></div>';
   message += '<div style="clear: both; padding-bottom: 1em;"></div>';
 
   var form = '<form id="userForm" method="post" onsubmit="submitUser(\'update\'); return false">';
@@ -47,14 +47,14 @@ function editUser() {
 }
 
 function confirmedDelete(login) {
-  return confirm('Warning!\n\nYou are going to permanently delete user "' + login + '", together with all their routes and positions.\n\nAre you sure?');
+  return confirm(sprintf(lang['deletewarn'], '"' + login + '"'));
 }
 
 function submitUser(action) {
   var form = document.getElementById('userForm');
   var login = form.elements['login'].value;
   if (!login) {
-      alert("All fields are required");
+      alert(lang['allrequired']);
       return;
   }
   var pass = null;
@@ -63,11 +63,11 @@ function submitUser(action) {
     pass = form.elements['pass'].value;
     pass2 = form.elements['pass2'].value;
     if (!pass || !pass2) {
-      alert("All fields are required");
+      alert(lang['allrequired']);
       return;
     }
     if (pass != pass2) {
-      alert("Passwords don't match");
+      alert(lang['passnotmatch']);
       return;
     }
   } else {
@@ -84,7 +84,7 @@ function submitUser(action) {
         var root = xml.getElementsByTagName('root');
         if (root.length && getNode(root[0], 'error') == 0) {
           removeModal();
-          alert("Action completed successfully");
+          alert(lang['actionsuccess']);
           if (action == 'delete') {
             // select current user in users form
             var f = document.getElementsByName('user')[0];
@@ -96,7 +96,7 @@ function submitUser(action) {
         errorMsg = getNode(root[0], 'message');
         if (errorMsg) { message = errorMsg; }
       }
-      alert("Something went wrong\n" + message);
+      alert(lang['actionfailure'] + '\n' + message);
       xhr = null;
     }
   }
diff --git a/js/main.js b/js/main.js
index 7a41fc9..d7d4688 100755
--- a/js/main.js
+++ b/js/main.js
@@ -384,7 +384,7 @@ function loadMapAPI(api) {
 var loadTime = 0;
 function waitAndLoad(api, url) {
   // wait till first script loaded
-  if (loadTime > 5000) { loadTime = 0; alert('Sorry, can\'t load ' + api + ' API'); return; }
+  if (loadTime > 5000) { loadTime = 0; alert(sprintf(lang['apifailure'], api)); return; }
   if (loadedAPI !== api) {
     setTimeout(function () { loadTime += 50; waitAndLoad(api, url); }, 50);
     return;
@@ -398,7 +398,7 @@ function waitAndLoad(api, url) {
 
 function waitAndInit(api) {
   // wait till main api loads
-  if (loadTime > 10000) { loadTime = 0; alert('Sorry, can\'t load ' + api + ' API'); return; }
+  if (loadTime > 10000) { loadTime = 0; alert(sprintf(lang['apifailure'], api)); return; }
   try {
     init();
   }
diff --git a/js/pass.js b/js/pass.js
index 0f92819..7e59688 100644
--- a/js/pass.js
+++ b/js/pass.js
@@ -32,11 +32,11 @@ function submitPass() {
   var pass = form.elements['pass'].value;
   var pass2 = form.elements['pass2'].value;
   if (!oldpass || !pass || !pass2) {
-    alert("All fields are required");
+    alert(lang['allrequired']);
     return;
   }
   if (pass != pass2) {
-    alert("Passwords don't match");
+    alert(lang['passnotmatch']);
     return;
   }
   var xhr = getXHR();
@@ -48,13 +48,13 @@ function submitPass() {
         var root = xml.getElementsByTagName('root');
         if (root.length && getNode(root[0], 'error') == 0) {
           removeModal();
-          alert("Password successfully changed");
+          alert(lang["actionsuccess"]);
           return;
         }
         errorMsg = getNode(root[0], 'message');
         if (errorMsg) { message = errorMsg; }
       }
-      alert("Something went wrong\n" + message);
+      alert(lang['actionfailure'] + '\n' + message);
       xhr = null;
     }
   }
diff --git a/lang/en.php b/lang/en.php
index 6563bcc..1f9e855 100644
--- a/lang/en.php
+++ b/lang/en.php
@@ -67,5 +67,14 @@ $lang["gps"] = "GPS";
 $lang["network"] = "Network";
 $lang["deluser"] = "Remove user";
 $lang["edituser"] = "Edit user";
+$lang["servererror"] = "Server error";
+$lang["allrequired"] = "All fields are required";
+$lang["passnotmatch"] = "Passwords don't match";
+$lang["actionsuccess"] = "Action completed successfully";
+$lang["actionfailure"] = "Something went wrong";
+$lang["deletewarn"] = "Warning!\n\nYou are going to permanently delete user %s, together with all their routes and positions.\n\nAre you sure?"; // substitutes user login
+$lang["editinguser"] = "You are editing user %s"; // substitutes user login
+$lang["selfeditwarn"] = "Your can't edit your own user with this tool";
+$lang["apifailure"] = "Sorry, can't load %s API"; // substitures api name (gmaps or openlayers)
 
 ?>
diff --git a/lang/pl.php b/lang/pl.php
index f8117e8..c58a1e0 100644
--- a/lang/pl.php
+++ b/lang/pl.php
@@ -65,5 +65,14 @@ $lang["gps"] = "GPS";
 $lang["network"] = "Sieć";
 $lang["deluser"] = "Usuń użytkownika";
 $lang["edituser"] = "Edytuj użytkownika";
+$lang["servererror"] = "Błąd serwera";
+$lang["allrequired"] = "Wszystkie pola są wymagane";
+$lang["passnotmatch"] = "Hasła nie pasują do siebie";
+$lang["actionsuccess"] = "Operacja zakończona pomyślnie";
+$lang["actionfailure"] = "Wystąpił błąd";
+$lang["deletewarn"] = "Uwaga!\n\nZamierzasz całkowicie usunąć użytkownika %s, razem ze wszystkimi jego trasami i pozycjami.\n\nCzy na pewno?";
+$lang["editinguser"] = "Edytujesz użytkownika %s";
+$lang["selfeditwarn"] = "Nie można edytować własnego użytkownika za pomocą tego narzędzia";
+$lang["apifailure"] = "Niestety ładowanie API %s nie powiodło się";
 
 ?>
diff --git a/utils/handleuser.php b/utils/handleuser.php
index 2193a10..4887df3 100644
--- a/utils/handleuser.php
+++ b/utils/handleuser.php
@@ -45,7 +45,7 @@
   $login = isset($_REQUEST['login']) ? trim($_REQUEST['login']) : NULL;
   $hash = isset($_REQUEST['pass']) ? password_hash($_REQUEST['pass'], PASSWORD_DEFAULT) : NULL;
   if (!$user->isAdmin || empty($action) || empty($login) || $user->login == $login) {
-    exitWithStatus(true, "Server error");
+    exitWithStatus(true, $lang["servererror"]);
   }
 
   $aUser = new uUser($login);
@@ -53,7 +53,7 @@
   switch ($action) {
     case 'add':
       if (empty($hash)) {
-        exitWithStatus(true, "Server error");
+        exitWithStatus(true, $lang["servererror"]);
       }
       if ($aUser->isValid) {
         exitWithStatus(true, $lang["userexists"]);
@@ -66,7 +66,7 @@
     case 'update':
       // update password
       if (empty($hash)) {
-        exitWithStatus(true, "Server error");
+        exitWithStatus(true, $lang["servererror"]);
       }
       if ($aUser->setPass($hash) === false) {
         exitWithStatus(true, $mysqli->error);
@@ -80,7 +80,7 @@
       break;
 
     default:
-      exitWithStatus(true, "Server error");
+      exitWithStatus(true, $lang["servererror"]);
       break;
   }