Optimizing LLMs for Italian: Reducing Token Fertility and Enhancing Efficiency Through Vocabulary Adaptation

Abstract

An increasing number of pretrained Large Language Models (LLMs) are being released, though the majority are predominantly designed for English. While they can often handle other languages due to contamination or some degree of multilingual pretraining data, English-centric LLMs are not optimized for non-English languages. This leads to inefficient encoding (high token ‘fertility’) and slower inference times for those languages. In this work, we explore various vocabulary adaptation techniques to tailor English LLMs for the Italian language. We introduce Semantic Alignment Vocabulary Adaptation (SAVA), a novel method that learns neural mapping to accomplish vocabulary substitution, which achieve state-of-the-art performances on several downstream tasks. We adapted two LLMs: Mistral-7b-v0.1, reducing token fertility by 25%, and Llama-3.1-8b, optimizing the vocabulary and reducing the number of parameters by 1 billion. We show that, after the adaptation of the vocabulary, these models can recover their performances with a relatively limited stage of continual training on the target language. Finally, we test the adapted models' capabilities on several multi-choice and generative tasks.