Adapting Chat Language Models Using Only Target Unlabeled Language Data

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Main Authors: Yamaguchi, Atsuki, Morishita, Terufumi, Villavicencio, Aline, Aletras, Nikolaos
Format: Preprint
Published: 2024
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author Yamaguchi, Atsuki
Morishita, Terufumi
Villavicencio, Aline
Aletras, Nikolaos
author_facet Yamaguchi, Atsuki
Morishita, Terufumi
Villavicencio, Aline
Aletras, Nikolaos
contents Vocabulary expansion (VE) is the de-facto approach to language adaptation of large language models (LLMs) by adding new tokens and continuing pre-training on target data. While this is effective for base models trained on unlabeled data, it poses challenges for chat models trained to follow instructions through labeled conversation data. Directly adapting the latter with VE on target unlabeled data may result in forgetting chat abilities. While ideal, target chat data is often unavailable or costly to create for low-resource languages, and machine-translated alternatives are not always effective. To address this issue, previous work proposed using a base and chat model from the same family. This method first adapts the base LLM with VE on target unlabeled data and then converts it to a chat model by adding a chat vector (CV) derived from the weight difference between the source base and chat models. We propose ElChat, a new language adaptation method for chat LLMs that adapts a chat model directly on target unlabeled data, without a base model. It elicits chat abilities by injecting information from the source chat model. ElChat offers more robust and competitive target language and safety performance while achieving superior English, chat, and instruction-following abilities compared to CV.
format Preprint
id arxiv_https___arxiv_org_abs_2412_11704
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle Adapting Chat Language Models Using Only Target Unlabeled Language Data
Yamaguchi, Atsuki
Morishita, Terufumi
Villavicencio, Aline
Aletras, Nikolaos
Computation and Language
Artificial Intelligence
Vocabulary expansion (VE) is the de-facto approach to language adaptation of large language models (LLMs) by adding new tokens and continuing pre-training on target data. While this is effective for base models trained on unlabeled data, it poses challenges for chat models trained to follow instructions through labeled conversation data. Directly adapting the latter with VE on target unlabeled data may result in forgetting chat abilities. While ideal, target chat data is often unavailable or costly to create for low-resource languages, and machine-translated alternatives are not always effective. To address this issue, previous work proposed using a base and chat model from the same family. This method first adapts the base LLM with VE on target unlabeled data and then converts it to a chat model by adding a chat vector (CV) derived from the weight difference between the source base and chat models. We propose ElChat, a new language adaptation method for chat LLMs that adapts a chat model directly on target unlabeled data, without a base model. It elicits chat abilities by injecting information from the source chat model. ElChat offers more robust and competitive target language and safety performance while achieving superior English, chat, and instruction-following abilities compared to CV.
title Adapting Chat Language Models Using Only Target Unlabeled Language Data
topic Computation and Language
Artificial Intelligence
url https://arxiv.org/abs/2412.11704