Bi-Text Mining across German Dialects: On the Role of Synthetic Training Data for Dialect Adaptation

Jing Wang, Barbara Plank, Robert Litschko


Abstract
Cross-dialect bi-text mining relies on robust multilingual sentence representations to identify semantically equivalent sentence pairs across languages. While recent multilingual bi-encoder models achieve strong performance on standardized written languages, their behavior on dialectal varieties is largely unknown. In this study, we use Tatoeba to evaluate the performance of four widely-used bi-encoders on dialect-to-standard German translation retrieval, covering German documents and queries written in three dialects: Low German, Bavarian, and Alemannic. Motivated by the lack of resources, we examine the extent to which synthetic translations (from dictionaries and large language models; LLMs) can serve as weak supervision for dialect adaptation. Our results reveal that bi-encoders, when applied in a zero-shot setting, exhibit deficiencies in capturing semantic similarity between German and dialects, while fine-tuning on synthetic data substantially improves their retrieval effectiveness, with larger gains obtained from LLM-translated training data. We further analyze retrieval performance on Bavarian across varying dialect word proportions and observe a drop when dialect words make up more than 60% of the text.
Anthology ID:
2026.bucc-1.9
Volume:
Proceedings of the 19th Workshop on Building and Using Comparable Corpora (BUCC)
Month:
May
Year:
2026
Address:
Palma de Mallorca, Spain
Editors:
Reinhard Rapp, Ayla Rigouts Terryn, Serge Sharoff, Pierre Zweigenbaum
Venues:
BUCC | WS
SIG:
Publisher:
ELRA Language Resources Association (ELRA)
Note:
Pages:
72–83
Language:
External URL:
https://lrec.elra.info/lrec2026-ws-bucc-09
DOI:
10.63317/3gmqhegz45cn
Bibkey:
Cite (ACL):
Jing Wang, Barbara Plank, and Robert Litschko. 2026. Bi-Text Mining across German Dialects: On the Role of Synthetic Training Data for Dialect Adaptation. In Proceedings of the 19th Workshop on Building and Using Comparable Corpora (BUCC), pages 72–83, Palma de Mallorca, Spain. ELRA Language Resources Association (ELRA).
Cite (Informal):
Bi-Text Mining across German Dialects: On the Role of Synthetic Training Data for Dialect Adaptation (Wang et al., BUCC 2026)
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