Do Llamas Work in English? On the Latent Language of Multilingual Transformers
Written for the Research library (claude-opus-5-5) from the paper text. Original — aclanthology.org/2024.acl-long.820.pdf
Summary
The paper asks whether multilingual LLMs trained mostly on English text silently route non-English processing through English. Using the open Llama-2 models (7B, 13B, 70B), the authors build non-English prompts for three tasks: translation, cloze and word repetition. Each prompt has exactly one correct single-token answer. They decode the last token's hidden state at every layer with the logit lens. They avoid the tuned lens on purpose, because its training would erase the signal they want to detect. They also analyse the latents geometrically as points in embedding space.
The forward pass shows three stages:
- Early layers decode nothing meaningful.
- Middle layers already reflect the correct meaning but prefer the English word over the target-language one.
- Late layers move into the region of the input language.
The authors read this as a path from an input space, through a "concept space" that leans toward English, to an output space. They argue this is a semantic bias, not an explicit translation step. This matters because such a bias could shape model behaviour in other languages and disadvantage less-resourced ones.
Key points
- Llama-2 was trained on about two trillion tokens, of which 89.70% are English. Small shares still amount to billions of tokens, for example roughly 3.4B German and 2.6B Chinese tokens.
- The three model sizes have 32/40/80 layers and a shared 32,000-token vocabulary. All were run with 8-bit quantization.
- Logit-lens decoding shows the English version of the answer peaking in middle layers before the correct target-language token takes over. One example is French "fleur" → Chinese "花", where "flower" appears first.
- The English detour is weaker on the repetition task and where words map to single tokens. The shares of single-token words were 100% for Chinese, 55% for French, 43% for German and 13% for Russian, which suggests tokenization plays a role.
- The study is limited to Llama-2, with initial evidence that Mistral-7B behaves the same way. Code and data are released at github.com/epfl-dlab/llm-latent-language.
Cited by
- Adapting LLMs to Hebrew: Unveiling DictaLM 2.0 with Enhanced Vocabulary and Instruction Capabilities
Cite
@inproceedings{wendler2024do,
title = {{Do Llamas Work in English? On the Latent Language of Multilingual Transformers}},
author = {Wendler, Chris and Veselovsky, Veniamin and Monea, Giovanni and West, Robert},
booktitle = {Proceedings of the 62nd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)},
year = {2024},
doi = {10.18653/v1/2024.acl-long.820},
url = {https://doi.org/10.18653/v1/2024.acl-long.820}
}References
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