diff --git a/Admin/Templates/config.tpl b/Admin/Templates/config.tpl
index 2be017d3..afd05a62 100644
--- a/Admin/Templates/config.tpl
+++ b/Admin/Templates/config.tpl
@@ -59,7 +59,7 @@ $editIcon = '<svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke=
     <tr><td><?php echo CONF_SERV_NAME ?> <em class="tooltip">?<span class="classic"><?php echo CONF_SERV_NAME_TOOLTIP ?></span></em></td><td><?php echo SERVER_NAME;?></td></tr>
     <tr><td><?php echo CONF_SERV_STARTED ?> <em class="tooltip">?<span class="classic"><?php echo CONF_SERV_STARTED_TOOLTIP ?></span></em></td><td><?php echo "Date:".START_DATE." Time:".START_TIME;?></td></tr>
     <tr><td><?php echo CONF_SERV_TIMEZONE ?> <em class="tooltip">?<span class="classic"><?php echo CONF_SERV_TIMEZONE_TOOLTIP ?></span></em></td><td><?php echo TIMEZONE;?></td></tr>
-    <tr><td><?php echo CONF_SERV_LANG ?> <em class="tooltip">?<span class="classic"><?php echo CONF_SERV_LANG_TOOLTIP ?></span></em></td><td><?php if(LANG == 'en') echo "English"; elseif(LANG == 'fr') echo "French"; elseif(LANG == 'es') echo "Spain"; elseif(LANG == 'rs') echo "Serbian"; elseif(LANG == 'ro') echo "Romanian"; elseif(LANG == 'zh_tw') echo "Taiwanese"; ?></td></tr>
+    <tr><td><?php echo CONF_SERV_LANG ?> <em class="tooltip">?<span class="classic"><?php echo CONF_SERV_LANG_TOOLTIP ?></span></em></td><td><?php if((defined('SERVER_LANG') ? SERVER_LANG : LANG) == 'en') echo "English"; elseif((defined('SERVER_LANG') ? SERVER_LANG : LANG) == 'fr') echo "French"; elseif((defined('SERVER_LANG') ? SERVER_LANG : LANG) == 'es') echo "Spain"; elseif((defined('SERVER_LANG') ? SERVER_LANG : LANG) == 'rs') echo "Serbian"; elseif((defined('SERVER_LANG') ? SERVER_LANG : LANG) == 'ro') echo "Romanian"; elseif((defined('SERVER_LANG') ? SERVER_LANG : LANG) == 'zh_tw') echo "Taiwanese"; ?></td></tr>
     <tr><td><?php echo CONF_SERV_SERVSPEED ?> <em class="tooltip">?<span class="classic"><?php echo CONF_SERV_SERVSPEED_TOOLTIP ?></span></em></td><td><?php echo ''.SPEED.'x';?></td></tr>
     <tr><td><?php echo CONF_SERV_TROOPSPEED ?> <em class="tooltip">?<span class="classic"><?php echo CONF_SERV_TROOPSPEED_TOOLTIP ?></span></em></td><td><?php echo INCREASE_SPEED;?>x</td></tr>
     <tr><td><?php echo CONF_SERV_EVASIONSPEED ?> <em class="tooltip">?<span class="classic"><?php echo CONF_SERV_EVASIONSPEED_TOOLTIP ?></span></em></td><td><?php echo EVASION_SPEED;?></td></tr>
diff --git a/Admin/Templates/editServerSet.tpl b/Admin/Templates/editServerSet.tpl
index 19ce86c9..787faf89 100644
--- a/Admin/Templates/editServerSet.tpl
+++ b/Admin/Templates/editServerSet.tpl
@@ -70,12 +70,12 @@ function refresh(tz) {
                         <td><?php echo CONF_SERV_LANG ?> <em class="tooltip">?<span class="classic"><?php echo CONF_SERV_LANG_TOOLTIP ?></span></em></td>
                         <td>
                             <select name="lang">
-                                <option value="en" <?php if (LANG=="en") echo "selected";?>>English</option>
-                                <option value="fr" <?php if (LANG=="fr") echo "selected";?>>French</option>
-                                <option value="es" <?php if (LANG=="es") echo "selected";?>>Spain</option>
-                                <option value="rs" <?php if (LANG=="rs") echo "selected";?>>Serbian</option>
-                                <option value="ru" <?php if (LANG=="ro") echo "selected";?>>Romanian</option>
-                                <option value="zh_tw" <?php if (LANG=="zh_tw") echo "selected";?>>Taiwanese</option>
+                                <option value="en" <?php if ((defined('SERVER_LANG') ? SERVER_LANG : LANG)=="en") echo "selected";?>>English</option>
+                                <option value="fr" <?php if ((defined('SERVER_LANG') ? SERVER_LANG : LANG)=="fr") echo "selected";?>>French</option>
+                                <option value="es" <?php if ((defined('SERVER_LANG') ? SERVER_LANG : LANG)=="es") echo "selected";?>>Spain</option>
+                                <option value="rs" <?php if ((defined('SERVER_LANG') ? SERVER_LANG : LANG)=="rs") echo "selected";?>>Serbian</option>
+                                <option value="ru" <?php if ((defined('SERVER_LANG') ? SERVER_LANG : LANG)=="ro") echo "selected";?>>Romanian</option>
+                                <option value="zh_tw" <?php if ((defined('SERVER_LANG') ? SERVER_LANG : LANG)=="zh_tw") echo "selected";?>>Taiwanese</option>
                             </select>
                         </td>
 					</tr>
diff --git a/GameEngine/Admin/Mods/editAdminInfo.php b/GameEngine/Admin/Mods/editAdminInfo.php
index 7653ec4b..534eebf6 100755
--- a/GameEngine/Admin/Mods/editAdminInfo.php
+++ b/GameEngine/Admin/Mods/editAdminInfo.php
@@ -73,7 +73,7 @@ $fh = fopen($myFile, 'w') or die("<br/><br/><br/>Can't open file: GameEngine\con
 		$text = preg_replace("'%STARTTIME%'", COMMENCE, $text);
 		$text = preg_replace("'%SSTARTDATE%'", START_DATE, $text);
 		$text = preg_replace("'%SSTARTTIME%'", START_TIME, $text);
-		$text = preg_replace("'%LANG%'", LANG, $text);
+		$text = preg_replace("'%LANG%'", (defined('SERVER_LANG') ? SERVER_LANG : LANG), $text);
 		$text = preg_replace("'%SPEED%'", SPEED, $text);
 		$text = preg_replace("'%MAX%'", WORLD_MAX, $text);
 		$text = preg_replace("'%GP%'", $GP_ENABLE, $text);
diff --git a/GameEngine/Admin/Mods/editExtraSet.php b/GameEngine/Admin/Mods/editExtraSet.php
index d14c4963..aca89d7a 100755
--- a/GameEngine/Admin/Mods/editExtraSet.php
+++ b/GameEngine/Admin/Mods/editExtraSet.php
@@ -72,7 +72,7 @@ $fh = fopen($myFile, 'w') or die("<br/><br/><br/>Can't open file: GameEngine\con
 		$text = preg_replace("'%STARTTIME%'", COMMENCE, $text);
 		$text = preg_replace("'%SSTARTDATE%'", START_DATE, $text);
 		$text = preg_replace("'%SSTARTTIME%'", START_TIME, $text);
-		$text = preg_replace("'%LANG%'", LANG, $text);
+		$text = preg_replace("'%LANG%'", (defined('SERVER_LANG') ? SERVER_LANG : LANG), $text);
 		$text = preg_replace("'%SPEED%'", SPEED, $text);
 		$text = preg_replace("'%MAX%'", WORLD_MAX, $text);
 		$text = preg_replace("'%GP%'", GP_ENABLE, $text);
diff --git a/GameEngine/Admin/Mods/editLogSet.php b/GameEngine/Admin/Mods/editLogSet.php
index 1b8c0b3c..ba66d739 100755
--- a/GameEngine/Admin/Mods/editLogSet.php
+++ b/GameEngine/Admin/Mods/editLogSet.php
@@ -68,7 +68,7 @@ $fh = fopen($myFile, 'w') or die("<br/><br/><br/>Can't open file: GameEngine\con
 		$text = preg_replace("'%STARTTIME%'", COMMENCE, $text);
 		$text = preg_replace("'%SSTARTDATE%'", START_DATE, $text);
 		$text = preg_replace("'%SSTARTTIME%'", START_TIME, $text);
-		$text = preg_replace("'%LANG%'", LANG, $text);
+		$text = preg_replace("'%LANG%'", (defined('SERVER_LANG') ? SERVER_LANG : LANG), $text);
 		$text = preg_replace("'%SPEED%'", SPEED, $text);
 		$text = preg_replace("'%MAX%'", WORLD_MAX, $text);
 		$text = preg_replace("'%GP%'", $GP_ENABLE, $text);
diff --git a/GameEngine/Admin/Mods/editNewFunctions.php b/GameEngine/Admin/Mods/editNewFunctions.php
index 0d8e56dc..9a331a60 100644
--- a/GameEngine/Admin/Mods/editNewFunctions.php
+++ b/GameEngine/Admin/Mods/editNewFunctions.php
@@ -41,7 +41,7 @@ $fh = fopen($myFile, 'w') or die("<br/><br/><br/>Can't open file: GameEngine\con
 		$text = preg_replace("'%STARTTIME%'", COMMENCE, $text);
 		$text = preg_replace("'%SSTARTDATE%'", START_DATE, $text);
 		$text = preg_replace("'%SSTARTTIME%'", START_TIME, $text);
-		$text = preg_replace("'%LANG%'", LANG, $text);
+		$text = preg_replace("'%LANG%'", (defined('SERVER_LANG') ? SERVER_LANG : LANG), $text);
 		$text = preg_replace("'%SPEED%'", SPEED, $text);
 		$text = preg_replace("'%MAX%'", WORLD_MAX, $text);
 		$text = preg_replace("'%GP%'", GP_ENABLE, $text);
diff --git a/GameEngine/Admin/Mods/editNewsboxSet.php b/GameEngine/Admin/Mods/editNewsboxSet.php
index 14c9988a..ab89c499 100755
--- a/GameEngine/Admin/Mods/editNewsboxSet.php
+++ b/GameEngine/Admin/Mods/editNewsboxSet.php
@@ -74,7 +74,7 @@ $fh = fopen($myFile, 'w') or die("<br/><br/><br/>Can't open file: GameEngine\con
 		$text = preg_replace("'%STARTTIME%'", COMMENCE, $text);
 		$text = preg_replace("'%SSTARTDATE%'", START_DATE, $text);
 		$text = preg_replace("'%SSTARTTIME%'", START_TIME, $text);
-		$text = preg_replace("'%LANG%'", LANG, $text);
+		$text = preg_replace("'%LANG%'", (defined('SERVER_LANG') ? SERVER_LANG : LANG), $text);
 		$text = preg_replace("'%SPEED%'", SPEED, $text);
 		$text = preg_replace("'%MAX%'", WORLD_MAX, $text);
 		$text = preg_replace("'%GP%'", $GP_ENABLE, $text);
diff --git a/GameEngine/Admin/Mods/editPlusSet.php b/GameEngine/Admin/Mods/editPlusSet.php
index a48b4b0b..48568067 100644
--- a/GameEngine/Admin/Mods/editPlusSet.php
+++ b/GameEngine/Admin/Mods/editPlusSet.php
@@ -56,7 +56,7 @@ $fh = fopen($myFile, 'w') or die("<br/><br/><br/>Can't open file: GameEngine\con
 		$text = preg_replace("'%STARTTIME%'", COMMENCE, $text);
 		$text = preg_replace("'%SSTARTDATE%'", START_DATE, $text);
 		$text = preg_replace("'%SSTARTTIME%'", START_TIME, $text);
-		$text = preg_replace("'%LANG%'", LANG, $text);
+		$text = preg_replace("'%LANG%'", (defined('SERVER_LANG') ? SERVER_LANG : LANG), $text);
 		$text = preg_replace("'%SPEED%'", SPEED, $text);
 		$text = preg_replace("'%MAX%'", WORLD_MAX, $text);
 		$text = preg_replace("'%GP%'", GP_ENABLE, $text);
diff --git a/GameEngine/Session.php b/GameEngine/Session.php
index 50524b77..8b524c46 100755
--- a/GameEngine/Session.php
+++ b/GameEngine/Session.php
@@ -369,6 +369,15 @@ function __construct() {
 	}
 		$this->userarray = $this->userinfo = $_SESSION[$cacheKeyUser]['data'];
 
+        // Per-user language (issue #166): seed the session language from the
+        // player's saved preference (users.lang) the first time, e.g. right
+        // after login. Once set, the profile "save preferences" page keeps it
+        // up to date, so we don't overwrite it here (also avoids reverting to
+        // a stale value from the 30s user cache above).
+        if (empty($_SESSION['lang']) && !empty($this->userarray['lang'])) {
+            $_SESSION['lang'] = $this->userarray['lang'];
+        }
+
         $this->username = $this->userarray['username'];
         $this->uid = $_SESSION['id_user'] = $this->userarray['id'];
 
diff --git a/install/data/constant_format.tpl b/install/data/constant_format.tpl
index 5221def8..369cbf86 100644
--- a/install/data/constant_format.tpl
+++ b/install/data/constant_format.tpl
@@ -43,8 +43,22 @@ define("START_DATE", "%SSTARTDATE%");
 define("START_TIME", "%SSTARTTIME%");
 
 // ***** Language
-// Choose your server language.
-define("LANG","%LANG%");
+// SERVER_LANG is the DEFAULT language of the server (chosen at install / in
+// the admin "Server Settings"). LANG is the EFFECTIVE display language.
+//
+// Per-user language (issue #166): if the logged-in player picked a language
+// in their profile preferences (stored in users.lang and mirrored into
+// $_SESSION['lang']), LANG becomes that language; otherwise LANG falls back
+// to SERVER_LANG.
+//
+// SECURITY: LANG is used in include("Lang/".LANG.".php"), so the value is
+// strictly sanitized to [a-z_] (no path traversal) and the target file MUST
+// exist, otherwise we fall back to the server default. This prevents Local
+// File Inclusion via a crafted session value.
+define("SERVER_LANG", "%LANG%");
+if (session_status() !== PHP_SESSION_ACTIVE) { @session_start(); }
+$__user_lang = isset($_SESSION['lang']) ? preg_replace('/[^a-z_]/', '', strtolower((string) $_SESSION['lang'])) : '';
+define("LANG", ($__user_lang !== '' && is_file(__DIR__ . "/Lang/" . $__user_lang . ".php")) ? $__user_lang : SERVER_LANG);
 
 // ***** Speed
 // Choose your server speed. NOTICE: Higher speed, more likely