AmanaMT: Translation Direction Predicts Automatic Metric Reliability

Isaac Thompson


Abstract
When machine translation (MT) metrics fail in low-resource settings, the field typically blames data scarcity. We show this diagnosis is often wrong using AmanaMT, a unified benchmark spanning 730,748 segments, 33 languages, three annotation tiers, and 10 metrics: the dominant predictor of metric unreliability is not resource level but domain mismatch and translation direction. Direction is the single largest predictor of between-language variance in metric reliability (η2dir = 0.309, nearly a third of between-language variance); morphological type is a substantially smaller main effect (η2morph = 0.073), though the joint direction×morphology cells account for η2cell = 0.618, capturing direction-specific morphological variation. Ukrainian’s near-zero COMET correlation is fully explained by a domain label (other, not news): a genre confound, not a language problem. Russian’s weak aggregate dissolves into clean per-year signals once stratified by WMT year, a textbook Simpson’s Paradox from pooling heterogeneous system generations. Neural metrics (MetricX-24, xCOMET, COMET) substantially outperform n-gram baselines at every tier; the gap is largest in morphologically complex and non-news settings where surface overlap is an especially poor proxy for adequacy.
Anthology ID:
2026.wmt-main.42
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:
747–764
Language:
URL:
https://aclanthology.org/2026.wmt-main.42/
DOI:
Bibkey:
Cite (ACL):
Isaac Thompson. 2026. AmanaMT: Translation Direction Predicts Automatic Metric Reliability. In Proceedings of the Eleventh Conference on Machine Translation, pages 747–764, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
AmanaMT: Translation Direction Predicts Automatic Metric Reliability (Thompson, WMT 2026)
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PDF:
https://aclanthology.org/2026.wmt-main.42.pdf