Synthetic Fluency: Hallucinations, Confabulations, and the Creation of IrishWords in LLM-Generated Translations

Sheila Castilho, Zoe Fitzsimmons, Claire Holton, Aoife Mc Donagh


Abstract
This study examines hallucinations in Large Language Model (LLM) translations into Irish, specifically focusing on instances where the models generate novel, non-existent words. We classify these hallucinations within verb and noun categories, identifying six distinct patterns among the latter. Additionally, we analyse whether these hallucinations adhere to Irish morphological rules and what linguistic tendencies they exhibit. Our findings show that while both GPT-4.o and GPT-4.o Mini produce similar types of hallucinations, the Mini model generates them at a significantly higher frequency. Beyond classification, the discussion raises speculative questions about the implications of these hallucinations for the Irish language. Rather than seeking definitive answers, we offer food for thought regarding the increasing use of LLMs and their potential role in shaping Irish vocabulary and linguistic evolution. We aim to prompt discussion on how such technologies might influence language over time, particularly in the context of low-resource, morphologically rich languages.
Anthology ID:
2025.mtsummit-1.22
Volume:
Proceedings of Machine Translation Summit XX: Volume 1
Month:
June
Year:
2025
Address:
Geneva, Switzerland
Editors:
Pierrette Bouillon, Johanna Gerlach, Sabrina Girletti, Lise Volkart, Raphael Rubino, Rico Sennrich, Ana C. Farinha, Marco Gaido, Joke Daems, Dorothy Kenny, Helena Moniz, Sara Szoc
Venue:
MTSummit
SIG:
Publisher:
European Association for Machine Translation
Note:
Pages:
287–299
Language:
URL:
https://preview.aclanthology.org/nschneid-patch-1/2025.mtsummit-1.22/
DOI:
Bibkey:
Cite (ACL):
Sheila Castilho, Zoe Fitzsimmons, Claire Holton, and Aoife Mc Donagh. 2025. Synthetic Fluency: Hallucinations, Confabulations, and the Creation of IrishWords in LLM-Generated Translations. In Proceedings of Machine Translation Summit XX: Volume 1, pages 287–299, Geneva, Switzerland. European Association for Machine Translation.
Cite (Informal):
Synthetic Fluency: Hallucinations, Confabulations, and the Creation of IrishWords in LLM-Generated Translations (Castilho et al., MTSummit 2025)
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PDF:
https://preview.aclanthology.org/nschneid-patch-1/2025.mtsummit-1.22.pdf