Can Language Neuron Intervention Reduce Non-Target Language Output?

Suchun Xie, Hwichan Kim, Shota Sasaki, Kosuke Yamada, Jun Suzuki


Abstract
Large language models (LLMs) often fail togenerate text in the intended target language,particularly in non-English interactions. Con-currently, recent work has explored LanguageNeuron Intervention (LNI) as a promising tech-nique for steering output language. In thispaper, we re-evaluate LNI in more practicalscenarios—specifically with instruction-tunedmodels and prompts that explicitly specify thetarget language. Our experiments show thatwhile LNI also shows potential in such practi-cal scenarios, its average effect is limited andunstable across models and tasks, with a 0.83%reduction in undesired language output and a0.1% improvement in performance. Our furtheranalysis identifies two key factors for LNI’slimitation: (1) LNI affects both the output lan-guage and the content semantics, making ithard to control one without affecting the other,which explains the weak performance gains. (2)LNI increases the target language token proba-bilities, but they often remain below the top-1generation threshold, resulting in failure to gen-erate the target language in most cases. Ourresults highlight both the potential and limi-tations of LNI, paving the way for future im-provements
Anthology ID:
2025.blackboxnlp-1.26
Volume:
Proceedings of the 8th BlackboxNLP Workshop: Analyzing and Interpreting Neural Networks for NLP
Month:
November
Year:
2025
Address:
Suzhou, China
Editors:
Yonatan Belinkov, Aaron Mueller, Najoung Kim, Hosein Mohebbi, Hanjie Chen, Dana Arad, Gabriele Sarti
Venues:
BlackboxNLP | WS
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Publisher:
Association for Computational Linguistics
Note:
Pages:
452–466
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URL:
https://preview.aclanthology.org/ingest-emnlp/2025.blackboxnlp-1.26/
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Bibkey:
Cite (ACL):
Suchun Xie, Hwichan Kim, Shota Sasaki, Kosuke Yamada, and Jun Suzuki. 2025. Can Language Neuron Intervention Reduce Non-Target Language Output?. In Proceedings of the 8th BlackboxNLP Workshop: Analyzing and Interpreting Neural Networks for NLP, pages 452–466, Suzhou, China. Association for Computational Linguistics.
Cite (Informal):
Can Language Neuron Intervention Reduce Non-Target Language Output? (Xie et al., BlackboxNLP 2025)
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https://preview.aclanthology.org/ingest-emnlp/2025.blackboxnlp-1.26.pdf