diff --git a/database/migrations/2026_10_06_000001_normalize_legacy_user_languages.php b/database/migrations/2026_10_06_000001_normalize_legacy_user_languages.php
new file mode 100644
index 000000000..1bcf3f577
--- /dev/null
+++ b/database/migrations/2026_10_06_000001_normalize_legacy_user_languages.php
@@ -0,0 +1,26 @@
+<?php
+
+use App\Util\Localization\Localization;
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\Facades\DB;
+
+return new class extends Migration
+{
+    /**
+     * Rewrite legacy short language codes stored on users (es, fr, de, ...)
+     * to their current locale-coded equivalents (es-ES, fr-FR, de-DE, ...).
+     *
+     * The lang/ directories and the Vue i18n message bundles were renamed to
+     * regional codes, so a user still holding a short code falls back to
+     * English and cannot match the language picker. Each legacy value is
+     * updated in place; rows already using a regional code are left untouched.
+     */
+    public function up(): void
+    {
+        foreach (Localization::LEGACY_LOCALE_MAP as $legacy => $current) {
+            DB::table('users')
+                ->where('language', $legacy)
+                ->update(['language' => $current]);
+        }
+    }
+};