Efficiently Adapting Pretrained Language Models To New Languages
Paper · 2023 · Zoltan Csaki, Pian Pawakapan, Urmish Thakker et al.
Summary
Open LLMs trained mostly on English often do poorly on lower-resource languages, and building a model for such a language from scratch requires more data and compute than is usually available. The authors propose a low-cost way to adapt an existing English LLM, a 13B GPT-2-style model, to Hungarian and Thai. The recipe has two parts. First, about 5,000 of the least useful tokens in the original vocabulary are replaced with tokens from a BPE tokenizer trained on the target language, and their embeddings are re-initialized. This keeps the vocabulary size unchanged while sharply reducing the number of tokens needed per word. Second, both continued pretraining and instruction tuning use bilingual data mixtures that combine English with the new language, which limits catastrophic forgetting. The adapted models keep their English benchmark scores roughly unchanged and improve substantially on the new languages. They match or beat open baselines such as Llama2-7B, XGLM-7.5B, mt0-xxl, PULI-GPT-3SX and openthaigpt-7b-chat. The approach matters for any team that wants a capable model for a lower-resource language without paying for full pretraining.
Key points
- Tokenizer change: About 10% of the 50k GPT-2 vocabulary is swapped for target-language tokens. Section 2.1 reports fertility gains of 42% for Hungarian and 73% for Thai, while the conclusion gives roughly 50% and 70%. This translates to about 2x faster training and inference for Hungarian and 3x for Thai, with little loss of English fertility.
- Main results: The HU PT + IT model reaches 54.9% on Hungarian multiple-choice, 64.3 F1 on QA and 9.2 ROUGE-2 on summarization, while scoring 58.0% on English multiple-choice. The TH PT + IT model reaches 49.9% on Thai multiple-choice, 48.9 F1 on QA and 12.5 BLEU on translation.
- Tokenizer ablation: Compared with the original GPT-2 tokenizer, the bilingual tokenizer equals or improves English and most Hungarian scores, for example 54.9% vs 50.8% on HU multiple-choice. Hungarian translation BLEU, however, drops from 8.8 to 6.1.
- Pretraining mix: Including English in the training data reduces forgetting and also helps Hungarian performance. Results with 25% and 50% English are about the same. Adapting the existing model for 30k steps beats a Hungarian model trained from scratch for 100k steps.
- Instruction-tuning mix: With no Hungarian instruction data, the model forgets Hungarian. Adding Hungarian helps, but the gains flatten once Hungarian makes up more than about 1% of the 2B-token instruction set.
Fields, topics and concepts
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 16,667 worksArtificial Intelligence · 16,194 worksArts and Humanities · 16,039 worksLanguage and Linguistics · 15,891 works
🧭 Topics 1Research subjects and languages the work is about.Language models & pretraining · 3,320 works
Cite
Cite as Zoltan Csaki, Pian Pawakapan, Urmish Thakker and Qiantong Xu. 2023. Efficiently Adapting Pretrained Language Models To New Languages. arXiv:2311.05741.
@misc{csaki2023efficiently,
title = {{Efficiently Adapting Pretrained Language Models To New Languages}},
author = {Zoltan Csaki, Pian Pawakapan, Urmish Thakker and Qiantong Xu},
year = {2023},
doi = {10.48550/arxiv.2311.05741},
eprint = {2311.05741},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2311.05741}
}References
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