A Post-trainer's Guide to Multilingual Training Data: Uncovering Cross-lingual Transfer Dynamics (2504.16677v1)

Abstract: In order for LLMs to be useful across the globe, they are fine-tuned to follow instructions on multilingual data. Despite the ubiquity of such post-training, a clear understanding of the dynamics that enable cross-lingual transfer remains elusive. This study examines cross-lingual transfer (CLT) dynamics in realistic post-training settings. We study two model families of up to 35B parameters in size trained on carefully controlled mixtures of multilingual data on three generative tasks with varying levels of complexity (summarization, instruction following, and mathematical reasoning) in both single-task and multi-task instruction tuning settings. Overall, we find that the dynamics of cross-lingual transfer and multilingual performance cannot be explained by isolated variables, varying depending on the combination of post-training settings. Finally, we identify the conditions that lead to effective cross-lingual transfer in practice.

Understanding Cross-lingual Transfer Dynamics in Multilingual Training Data

The paper "A Post-trainer's Guide to Multilingual Training Data: Uncovering Cross-lingual Transfer Dynamics" conducts a rigorous examination of the cross-lingual transfer (CLT) dynamics critical for developing efficient and robust multilingual LLMs. The paper investigates these dynamics by focusing on multilingual post-training settings, leveraging models of various scales and training configurations to determine how different variables impact cross-lingual performance.

Key Findings

1. Task-Dependent Multilingual Performance: The paper reveals that multilingual data improves performance, but the effectiveness varies per task. Mathematical reasoning, in particular, benefits significantly from additional multilingual data, with performance gains stretching up to a notable 22.7%, unlike summarization and instruction-following tasks which plateau after limited exposure.
2. Efficiency of Scaling: Larger models demonstrate more efficient CLT capabilities, effectively narrowing the performance gap between seen and unseen languages. It is indicated that performance gains can be substantially realized with predominantly English data, supplemented by little multilingual data.
3. Single vs. Multi-task Dynamics: Training models on a multi-task setting introduces unique dynamics where interference between tasks can cause performance fluctuations. However, this interference diminishes for larger models, suggesting that scaling mitigates multi-task training challenges.
4. Optimal Language Mixture: The paper underscores that different tasks benefit from varying language mixtures; linguistically oriented tasks require more diverse script data, whereas reasoning tasks are more efficiently trained on Latin scripts.
5. Performance Plateau in Unseen Languages: Despite CLT aiding unseen language improvements, the research indicates a persisting performance gap compared to seen languages, which underscores potential limitations in current CLT applications.

Implications and Future Directions

The findings have significant implications for the development of multilingual LLMs. Understanding task-specific data requirements and exploiting large-scale models could lead to more effective cross-linguistic capabilities. The inherent inability to eliminate the performance differential for unseen languages while achieving near-English level performance on seen languages suggests areas needing further exploration, such as novel architecture designs or enhanced language-agnostic training methods.

Speculation on Future AI Developments

Future research can build on these foundations by exploring fine-tuning strategies with smaller data samples from resource-scarce languages, heading towards a more equitable language representation in AI systems. Furthermore, enhancing current evaluation metrics to capture nuanced task-specific multilingual performance will be crucial for aligning model output capabilities across languages.

In summary, this paper offers valuable insights into multilingual post-training dynamics, elucidating how model scale, task type, and language diversity influence CLT in current AI developments. It paves the way for advanced methodologies and architectural innovations to build superior multilingual LLMs.