Testing the Boundaries of LLMs: Dialectal and Language-Variety Tasks

Fahim Faisal, Antonios Anastasopoulos


Abstract
This study evaluates the performance of large language models (LLMs) on benchmark datasets designed for dialect-specific NLP tasks. Dialectal NLP is a low-resource field, yet it is crucial for evaluating the robustness of language models against linguistic diversity. This work is the first to systematically compare state-of-the-art instruction-tuned LLMs—both open-weight multilingual and closed-weight generative models—with encoder-based models that rely on supervised task-specific fine-tuning for dialectal tasks. We conduct extensive empirical analyses to provide insights into the current LLM landscape for dialect-focused tasks. Our findings indicate that certain tasks, such as dialect identification, are challenging for LLMs to replicate effectively due to the complexity of multi-class setups and the suitability of these tasks for supervised fine-tuning. Additionally, the structure of task labels—whether categorical or continuous scoring—significantly affects model performance. While LLMs excel in tasks like machine reading comprehension, their instruction-following ability declines in simpler tasks like POS tagging when task instructions are inherently complex. Overall, subtle variations in prompt design can greatly impact performance, underscoring the need for careful prompt engineering in dialectal evaluations.
Anthology ID:
2025.vardial-1.6
Volume:
Proceedings of the 12th Workshop on NLP for Similar Languages, Varieties and Dialects
Month:
January
Year:
2025
Address:
Abu Dhabi, UAE
Editors:
Yves Scherrer, Tommi Jauhiainen, Nikola Ljubešić, Preslav Nakov, Jorg Tiedemann, Marcos Zampieri
Venues:
VarDial | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
68–92
Language:
URL:
https://aclanthology.org/2025.vardial-1.6/
DOI:
Bibkey:
Cite (ACL):
Fahim Faisal and Antonios Anastasopoulos. 2025. Testing the Boundaries of LLMs: Dialectal and Language-Variety Tasks. In Proceedings of the 12th Workshop on NLP for Similar Languages, Varieties and Dialects, pages 68–92, Abu Dhabi, UAE. Association for Computational Linguistics.
Cite (Informal):
Testing the Boundaries of LLMs: Dialectal and Language-Variety Tasks (Faisal & Anastasopoulos, VarDial 2025)
Copy Citation:
PDF:
https://aclanthology.org/2025.vardial-1.6.pdf