多语言推理场景下，翻译不是越多越好——Luar 教会模型在「不懂的时候才翻」，做多语言 NLP 或低资源语言应用的团队可以直接用这个框架来提升推理效率。
推理语言模型在复杂推理任务上表现优异，但在非英语输入上仍存在多语言推理差距，主要原因是语言理解失败。英语翻译可以缓解这一问题，但并非所有输入都需要翻译。为此，研究者提出 Luar（语言理解边界感知强化学习框架），训练模型在直接理解不可靠时选择性调用翻译。在多项多语言推理基准测试中，Luar 优于标准 GRPO 等方法，尤其在低资源语言上提升显著。该框架能避免不必要的翻译，并泛化到未见过的低资源语言。项目代码已开源。
Learning When to Translate for Multilingual Reasoning
Reasoning language models (RLMs) achieve strong performance on complex reasoning tasks, but still exhibit substantial multilingual reasoning gaps, largely due to language-understanding failures in non-English inputs. English translation can mitigate these failures by expressing non-English inputs in a form that RLMs can more reliably interpret, yet translating every input is unnecessary when the model can reason reliably from the original query. To address this challenge, we propose Luar, a Language Understanding Boundary-aware Reinforcement Learning framework that trains RLMs to selectively invoke translation when direct understanding is unreliable. Luar trains the model to choose between solving the original input directly and reasoning over its English translation, encouraging translation only when translator-augmented reasoning is expected to substantially outperform direct reasoning. Across multilingual reasoning benchmarks, Luar outperforms standard GRPO and other training-based baselines, with particularly large gains on low-resource languages. Further analysis shows that Luar avoids unnecessary translation in cases where direct reasoning is sufficient, while extending its translator-call behavior to unseen low-resource languages. Together, our work suggests a selective approach to multilingual reasoning: RLMs can learn to invoke translation only when their direct understanding is unreliable. The project will be made publicly available at https://github.com/deokhk/LUAR