“落單”在英文中有多種譯法，具體取決于上下文和語氣：

**常用翻譯：**
1. **Left alone** - 強調被留下、被孤立
- 孩子們都走了，他一個人落單了。
- The children all left, and he was left alone.

2. **Be alone** - 狀態描述，單獨一人
- 深夜她不敢落單走路。
- She dare not walk alone at night.

**其他情景對應譯法：**
- **孤立無援** → Stranded/Isolated
- 登山隊中他落單了。
- He got separated from the hiking team.

- **掉隊** → Fall behind
- 行軍途中有人落單了。
- Someone fell behind during the march.

- **單身狀態** → Single/Available
- 派對上只有她落單。
- She was the only single one at the party.

**口語化表達：**
- "Third wheel" - 電燈泡（特指情侶間的落單者）
- "Odd one out" - 格格不入的人

需要根據具體場景選擇最貼切的翻譯，您能提供更多上下文嗎？我可以為您精準匹配表達。