diff --git a/database/migrations/2026_06_12_093000_backfill_machine_display_languages.php b/database/migrations/2026_06_12_093000_backfill_machine_display_languages.php
new file mode 100644
index 0000000..5fcb8fa
--- /dev/null
+++ b/database/migrations/2026_06_12_093000_backfill_machine_display_languages.php
@@ -0,0 +1,47 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\Facades\DB;
+
+return new class extends Migration
+{
+    /**
+     * 回填既有機台的顯示語系：將尚未設定 settings.languages 的機台補為
+     * ["zh_TW","en","ja"]，使既有 demo/prod 行為與現況一致 —— 公司機台語系
+     * 聯集維持中英日，商品編輯器照常顯示三 Tab，機台 B014 LangSet 亦得中英日。
+     *
+     * 僅補「缺鍵或空值」者，已設定者不動。直接以 DB 更新避免觸發 Machine 事件
+     * （MQTT 同步等）與全域範圍。
+     */
+    public function up(): void
+    {
+        $default = ['zh_TW', 'en', 'ja'];
+
+        DB::table('machines')->select('id', 'settings')->orderBy('id')
+            ->chunkById(200, function ($machines) use ($default) {
+                foreach ($machines as $m) {
+                    $settings = $m->settings ? json_decode($m->settings, true) : [];
+                    if (!is_array($settings)) {
+                        $settings = [];
+                    }
+                    // 已有非空 languages 者跳過
+                    if (!empty($settings['languages']) && is_array($settings['languages'])) {
+                        continue;
+                    }
+                    $settings['languages'] = $default;
+                    DB::table('machines')->where('id', $m->id)->update([
+                        'settings' => json_encode($settings, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES),
+                    ]);
+                }
+            });
+    }
+
+    /**
+     * 不反向移除 languages：無法區分回填值與使用者後續手動設定值，
+     * 貿然移除恐誤刪設定，故 down 不動資料。
+     */
+    public function down(): void
+    {
+        // no-op
+    }
+};
diff --git a/resources/views/admin/products/edit.blade.php b/resources/views/admin/products/edit.blade.php
index a4f3651..1f56708 100644
--- a/resources/views/admin/products/edit.blade.php
+++ b/resources/views/admin/products/edit.blade.php
@@ -6,6 +6,15 @@
     $localeLabels = config('locales.supported', ['zh_TW' => '繁體中文']);
     $locales = \App\Models\System\Company::activeLocalesFor($product->company_id);
 
+    // 保險：併入「此商品已有翻譯」的語系，避免公司聯集縮減時藏掉既有翻譯而無法編輯。
+    $existingLocales = $product->translations->pluck('locale')
+        ->merge($product->specTranslations->pluck('locale'))
+        ->unique()->all();
+    $order = array_keys($localeLabels); // 依白名單順序穩定排序
+    $locales = collect($locales)->merge($existingLocales)->unique()
+        ->sortBy(fn ($l) => ($i = array_search($l, $order)) === false ? 999 : $i)
+        ->values()->all();
+
     $names = [];
     $specs = [];
     foreach ($locales as $locale) {