“累旬”在中文里是一個相對少見的書面用語，意為“連續多日”或“長達數十天”。根據具體語境，其英文翻譯可以選用：

1. **for dozens of days**
（直譯，強調“數十天”的時間跨度）
*例句：大雨累旬，導致河流水位暴漲。*
→ It rained **for dozens of days**, causing the river water level to rise rapidly.

2. **for tens of days**
（直譯，稍顯生硬但準確）

3. **for many consecutive days**
（更自然的表達，強調“連續”）
*例句：他累旬伏案工作，終于完成了書稿。*
→ He worked at his desk **for many consecutive days** and finally completed the manuscript.

4. **over several weeks**
（意譯，若“旬”泛指較長時間）
*例句：談判累旬未果。*
→ The negotiations dragged on **over several weeks** without results.

**根據上下文選擇最貼切的譯法**，若需精確幫助，請提供完整句子。