Copy First, Translate Later: Interpreting Translation Dynamics in Multilingual Pretraining

Felicia Körner, Maria Matveev, Florian Eichin, Gitta Kutyniok, Barbara Plank, Michael A. Hedderich


Abstract
Large language models exhibit impressive cross-lingual capabilities. However, *how* cross-lingual generalization emerges has only been analyzed through isolated factors and at sparse points during training, limiting our understanding — particularly of the early phases of learning. To study the early trajectory of linguistic and translation capabilities, we pretrain a multilingual 1.7B model on nine diverse languages, capturing checkpoints at a much finer granularity. We use word-level translation as a testbed, introducing a novel dataset to trace how translation develops over training through behavioral analyses, model-component analysis, and parameter-based ablations. We find that the model quickly acquires basic linguistic capabilities in parallel with token-level copying, while translation develops in two distinct phases: an initial phase dominated by copying and surface-level similarities, and a second phase in which generalizing translation mechanisms develop and copying is refined. Together, these findings provide a fine-grained view of how cross-lingual generalization develops during multilingual pretraining.
Anthology ID:
2026.emnlp-main.2684
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
61018–61051
Language:
URL:
https://aclanthology.org/2026.emnlp-main.2684/
DOI:
Bibkey:
Cite (ACL):
Felicia Körner, Maria Matveev, Florian Eichin, Gitta Kutyniok, Barbara Plank, and Michael A. Hedderich. 2026. Copy First, Translate Later: Interpreting Translation Dynamics in Multilingual Pretraining. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 61018–61051, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Copy First, Translate Later: Interpreting Translation Dynamics in Multilingual Pretraining (Körner et al., EMNLP 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.emnlp-main.2684.pdf