Small Models, Big Impact: Efficient Corpus and Graph-Based Adaptation of
  Small Multilingual Language Models for Low-Resource Languages
Authors: name: Daniil Gurgurov, name: Ivan Vykopal, name: Josef van Genabith, name: Simon Ostermann

Low-resource languages (LRLs) face significant challenges in natural language
processing (NLP) due to limited data. While current state-of-the-art large
language models (LLMs) still struggle with LRLs, smaller multilingual models
(mLMs) such as mBERT and XLM-R offer greater promise due to a better fit of
their capacity to low training data sizes. This study systematically
investigates parameter-efficient adapter-based methods for adapting mLMs to
LRLs, evaluating three architectures: Sequential Bottleneck, Invertible
Bottleneck, and Low-Rank Adaptation. Using unstructured text from GlotCC and
structured knowledge from ConceptNet, we show that small adaptation datasets
(e.g., up to 1 GB of free-text or a few MB of knowledge graph data) yield gains
in intrinsic (masked language modeling) and extrinsic tasks (topic
classification, sentiment analysis, and named entity recognition). We find that
Sequential Bottleneck adapters excel in language modeling, while Invertible
Bottleneck adapters slightly outperform other methods on downstream tasks due
to better embedding alignment and larger parameter counts. Adapter-based
methods match or outperform full fine-tuning while using far fewer parameters,
and smaller mLMs prove more effective for LRLs than massive LLMs like LLaMA-3,
GPT-4, and DeepSeek-R1-based distilled models. While adaptation improves
performance, pre-training data size remains the dominant factor, especially for
languages with extensive pre-training coverage.