PragmaSpan at WMT26: Taxonomy-Guided Few-Shot Error Span Detection and an Empirical Analysis of MPP

Soyoung Lee


Abstract
We present PragmaSpan, a training-free, few-shot GPT-5.5 error-span detector with a seven-axis diagnostic taxonomy for WMT26 Task 1, wrapped in a reliability-oriented harness using incomplete-response-aware retries, deterministic parsing, offset recovery, exact-span deduplication, and independent artifact validation. The taxonomy provides a domain-sensitive diagnostic representation: its interpersonal and discourse axes track domain conversationality and match gold errors at least as often as its traditional axes, with no significant detection-F difference from a standard Multidimensional Quality Metrics (MQM) category tree. We use the system to characterize the severity-weighted Match with Partial overlap and Partial credit (MPP) metric. Across prompt and model comparisons, human-agreement calibration, and post-hoc refinement, we find (i) prompt variants do not differ significantly on our sample, while GPT-4.1-to-GPT-5.5 gains exceed differences among variants; (ii) human–human MPP is low on our multi-annotator surrogate sample, and system–human agreement is not significantly different from this empirical baseline; (iii) improvements in matched-pair severity or boundary accuracy can coincide with lower MPP, demonstrating the need to interpret MPP jointly with matched-pair diagnostics and match coverage; and (iv) a calibration gain on a single-annotator MQM benchmark does not replicate on a multi-annotator Error Span Annotation benchmark. Interpreting error-span improvements therefore requires complementary metrics and annotation-regime checks.
Anthology ID:
2026.wmt-main.101
Volume:
Proceedings of the Eleventh Conference on Machine Translation
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Barry Haddow, Tom Kocmi, Philipp Koehn, Christof Monz
Venues:
WMT | WS
SIG:
SIGMT
Publisher:
Association for Computational Linguistics
Note:
Pages:
1678–1688
Language:
URL:
https://aclanthology.org/2026.wmt-main.101/
DOI:
Bibkey:
Cite (ACL):
Soyoung Lee. 2026. PragmaSpan at WMT26: Taxonomy-Guided Few-Shot Error Span Detection and an Empirical Analysis of MPP. In Proceedings of the Eleventh Conference on Machine Translation, pages 1678–1688, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
PragmaSpan at WMT26: Taxonomy-Guided Few-Shot Error Span Detection and an Empirical Analysis of MPP (Lee, WMT 2026)
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PDF:
https://aclanthology.org/2026.wmt-main.101.pdf