Cross-Lingual Legal QA for Vietnamese Labour Law: Retrieval, Translation, and Verifier-Guided Correction

Nguyen Minh Chi, Mo El-Haj, Nguyen Ha Thanh, Dawn Knight, Paul Rayson


Abstract
Cross-lingual legal question answering must retrieve statutes across languages while preventing unsupported legal claims. We introduce a bilingual evaluation suite of 231 Vietnamese–English question–answer pairs from Vietnamese labour law. Of these, 75 questions are additionally annotated for five challenging legal reasoning phenomena. We evaluate a verifier-guided pipeline that decomposes answers into claims, checks citation reachability and entailment, and corrects citation failures and contradictions. We also introduce six automatic diagnostics of faithfulness to retrieved evidence, covering citations, modality, exceptions, procedures, conclusions, and evidential support. Experiments show that learned-sparse retrieval performs poorly for English-to-Vietnamese retrieval (R@5 = 0.032), whereas dense retrieval reaches 0.358 and slightly outperforms hybrid retrieval. Translation placement has no statistically detectable effect on these automatic diagnostics in our controlled comparison and supporting sensitivity analyses. Verifier-guided correction improves citation preservation by 0.022–0.034 at the system level but produces no reliable gains on the remaining dimensions. Human evaluation further highlights weaknesses that are not fully captured by automatic diagnostics, particularly in procedural completeness and the coverage of legally required conditions and steps.
Anthology ID:
2026.nllp-1.21
Volume:
Proceedings of the Natural Legal Language Processing Workshop 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Nikolaos Aletras, Ilias Chalkidis, Leslie Barrett, Cătălina Goanță, Daniel Preoțiuc-Pietro, Gerasimos Spanakis, Shanshan Xu
Venues:
NLLP | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
257
Language:
URL:
https://aclanthology.org/2026.nllp-1.21/
DOI:
Bibkey:
Cite (ACL):
Nguyen Minh Chi, Mo El-Haj, Nguyen Ha Thanh, Dawn Knight, and Paul Rayson. 2026. Cross-Lingual Legal QA for Vietnamese Labour Law: Retrieval, Translation, and Verifier-Guided Correction. In Proceedings of the Natural Legal Language Processing Workshop 2026, pages 257–257, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Cross-Lingual Legal QA for Vietnamese Labour Law: Retrieval, Translation, and Verifier-Guided Correction (Chi et al., NLLP 2026)
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PDF:
https://aclanthology.org/2026.nllp-1.21.pdf