Add per-user language selection (issue #166)

The profile already had a language selector (Templates/Profile/preference.tpl)
that saved the choice into users.lang and $_SESSION['lang'], but the saved
preference was never used to actually load the language: every page loads
include("Lang/".LANG.".php") with the server-wide LANG constant, so changing
the language in the profile had no visible effect.

This wires it up:

- Introduce SERVER_LANG (the server default) and make LANG the EFFECTIVE
  display language, resolved from the player's saved preference
  ($_SESSION['lang']) with a fallback to SERVER_LANG
  (install/data/constant_format.tpl).
  SECURITY: the value is sanitized to [a-z_] and the target Lang/<x>.php
  file must exist, otherwise we fall back to the server default. This
  prevents Local File Inclusion via include("Lang/".LANG.".php").

- Seed $_SESSION['lang'] from users.lang on login (GameEngine/Session.php,
  PopulateVar), so the chosen language applies right after logging in.

- Keep the SERVER default intact when an admin saves settings: the admin
  config regenerators and the "Server Settings"/config displays now use
  SERVER_LANG (the server default) instead of the per-user LANG, so an
  admin browsing in their own language can't accidentally overwrite the
  server default (6 Admin/Mods/edit*.php + editServerSet.tpl + config.tpl).

Note: existing installs must also add SERVER_LANG + the LANG resolution to
their generated GameEngine/config.php (and the Admin/Mods/constant_format.tpl
copy) since config is generated at install time.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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);

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);

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);

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);

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);

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);

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'];