Rule-Based Perturbation, Real Evaluation: How Far Do Fine-Tuned Encoders Go on Chinese Phonetically Cloaked Toxic Language?

Minggui Duan, Shijie Liu


Abstract
Phonetic cloaking, the deliberate use of homophones, Pinyin, and numeric substitutions to disguise toxic content, poses a persistent challenge to Chinese toxic language detection. Existing work mainly relies on rule-based synthetic perturbations for benchmark evaluation, leaving uncertain how well such results transfer to naturally occurring cloaking. We present a controlled evaluation of fine-tuned encoders on PCR-ToxiCN, a dataset of naturally occurring, phonetically cloaked Chinese posts. Fine-tuning ChineseBERT and RoBERTa-wwm-ext on the CNTP synthetic perturbation dataset, we quantify synthetic-to-real performance gaps across four cloaking strategies. Synthetic perturbation training produces consistent but limited improvements, with diminishing returns as perturbation coverage expands. Hanzi (Chinese-character) replacement remains consistently difficult for both encoders, and few-shot fine-tuning on roughly 50 real examples provides only marginal improvement. The few-shot experiment, however, cannot distinguish representation limits from data scarcity or sampling effects. Overall, our findings caution against equating synthetic benchmark performance with real-world robustness.
Anthology ID:
2026.woah-1.29
Volume:
Proceedings of the 10th Workshop on Online Abuse and Harms (WOAH)
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Agostina Calabrese, Thomas Davidson, Christine de Kock, Urja Khurana, Marta Marchiori Manerba, Paloma Piot, Zeerak Talat
Venues:
WOAH | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
338–345
Language:
URL:
https://aclanthology.org/2026.woah-1.29/
DOI:
Bibkey:
Cite (ACL):
Minggui Duan and Shijie Liu. 2026. Rule-Based Perturbation, Real Evaluation: How Far Do Fine-Tuned Encoders Go on Chinese Phonetically Cloaked Toxic Language?. In Proceedings of the 10th Workshop on Online Abuse and Harms (WOAH), pages 338–345, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Rule-Based Perturbation, Real Evaluation: How Far Do Fine-Tuned Encoders Go on Chinese Phonetically Cloaked Toxic Language? (Duan & Liu, WOAH 2026)
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PDF:
https://aclanthology.org/2026.woah-1.29.pdf
Supplementarymaterial:
 2026.woah-1.29.SupplementaryMaterial.zip