“塞子未开的”可以翻译为 "unopened (with the stopper/plug intact)" 或 "sealed (with the stopper/plug still on)"。
"Unopened" 强调物品（如瓶子、容器等）未被打开过，塞子或盖子仍处于原始关闭状态。
"Sealed" 则更侧重于物品被密封的状态，塞子或盖子完好无损。
根据具体语境，可以选择更贴切的表述。例如：
这瓶酒塞子未开，保存得很好。（This bottle of wine is unopened and well-preserved with the cork intact.）
这罐饮料塞子未开，还是满的。（This can of beverage is sealed with the plug still on and is still full.）