eBLEU: Unexpectedly Good Machine Translation Evaluation Using Simple Word Embeddings

Muhammad N. ElNokrashy, Tom Kocmi

Abstract: We propose eBLEU, a metric inspired by BLEU metric that uses embedding similarities instead of string matches. We introduce meaning diffusion vectors to enable matching n-grams of semantically similar words in a BLEU-like algorithm, using efficient, non-contextual word embeddings like fastText. On WMT23 data, eBLEU beats BLEU and ChrF by around 3.8% system-level score, approaching BERTScore at −0.9% absolute difference. In WMT22 scenarios, eBLEU outperforms f101spBLEU and ChrF in MQM by 2.2%−3.6%. Curiously, on MTurk evaluations, eBLEU surpasses past methods by 3.9%−8.2% (f200spBLEU, COMET-22). eBLEU presents an interesting middle-ground between traditional metrics and pretrained metrics.