Orthogonal Style Injection: Mechanistic Persona Steering for Zero-Shot Cross-Lingual Subtitle Translation

Tarun Chintada, Kshetrimayum Boynao Singh, Asif Ekbal


Abstract
In conversational and cinematic subtitle translation, large language models often exhibit stylistic collapse, defaulting to neutral registers that flatten character-specific personas. Prompt-based attempts to recover style frequently introduce instruction drift and semantic degradation. We propose Orthogonal Style Injection (OSI), a parameter-efficient, inference-time intervention that removes global stylistic bias through orthogonal projection at an intermediate layer and injects a character-specific style vector derived solely from English source dialogue. We evaluate OSI for English-to-Bengali, Hindi, Telugu, Tamil, Kannada, Chinese, Japanese, Spanish, French, German, and Italian subtitle translation, spanning 11 typologically diverse target languages. Results show that zero-shot stylistic transfer depends strongly on pretraining alignment. Llama-3.1-8B yields gains in several European languages but degrades on Indic languages, whereas Qwen-2.5-7B transfers style more robustly across Indic and East Asian languages. To probe sociolinguistic mechanisms, we curate a parallel English-Bengali cinematic dataset as a focused morphological stress test. Automatic metrics and human evaluation show that OSI enables meaningful honorific and register shifts while largely preserving semantic fidelity, revealing a dataset-dependent trade-off between stylistic fidelity and translation quality in highly colloquial, morphologically constrained settings.
Anthology ID:
2026.aacl-long.274
Volume:
Proceedings of the 15th International Joint Conference on Natural Language Processing and the 5th Conference of the Asia-Pacific Chapter of the Association for Computational Linguistics (Volume 1: Long Papers)
Month:
November
Year:
2026
Address:
Hengqin, China
Editors:
Yue Zhang, Ruifeng Xu, Ayu Purwarianti, Tong Rong, Jun Suzuki
Venues:
AACL | IJCNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
6058–6084
Language:
URL:
https://aclanthology.org/2026.aacl-long.274/
DOI:
Bibkey:
Cite (ACL):
Tarun Chintada, Kshetrimayum Boynao Singh, and Asif Ekbal. 2026. Orthogonal Style Injection: Mechanistic Persona Steering for Zero-Shot Cross-Lingual Subtitle Translation. In Proceedings of the 15th International Joint Conference on Natural Language Processing and the 5th Conference of the Asia-Pacific Chapter of the Association for Computational Linguistics (Volume 1: Long Papers), pages 6058–6084, Hengqin, China. Association for Computational Linguistics.
Cite (Informal):
Orthogonal Style Injection: Mechanistic Persona Steering for Zero-Shot Cross-Lingual Subtitle Translation (Chintada et al., AACL-IJCNLP 2026)
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PDF:
https://aclanthology.org/2026.aacl-long.274.pdf