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Breaking Physical and Linguistic Borders: Multilingual Federated Prompt Tuning for Low-Resource Languages
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Proposes multilingual federated prompt tuning, training only prompt encoders (or LoRA) on XLM-R base with FedAvg-style aggregation across language clients, evaluated on NC, XNLI and MasakhaNEWS for low-resource languages.
Problem
Fine-tuning multilingual LLMs for low-resource languages is hindered by data-sharing restrictions across regions, linguistic differences (non-IID), limited compute, and scarce data.
Approach
Combine federated averaging with parameter-efficient prompt tuning so each language/country client trains only a small virtual-token prompt encoder while the PLM stays frozen, and analyze gains via a language-distance metric defined as negative log cosine similarity to a token-weighted average pre-training language vector.
Key results
- On XNLI, federated prompt tuning averages 39.83% accuracy vs 32.94% for PE monolingual fine-tuning.
- On NC, PE_FL (IID) reaches 83.6% average vs 64.3% for PE monolingual.
- Communication reduced from 108 GB to 478.93 MB (about 99%) with a 2x768 prompt encoder under 5 clients and 10 rounds.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use federated prompt tuning instead of PE_Monolingual | XLM-RoBERTa base · XNLI | average accuracy: 32.94 -> 39.83 | Helped |
| Use federated prompt tuning in the IID setting instead of PE_Centralized | XLM-RoBERTa base · News Classification (NC) | average accuracy: 77.5 -> 83.6 | Helped |
| Use federated prompt tuning in the Non-IID setting instead of PE_Centralized | XLM-RoBERTa base · News Classification (NC) | average accuracy: 77.5 -> 80.7 | Helped |
| Use federated prompt tuning instead of PE_Centralized | XLM-RoBERTa base · MasakhaNEWS | average accuracy: 79.3 -> 76.4 | Hurt |
| Use federated LoRA instead of PE_Centralized | XLM-RoBERTa base · MasakhaNEWS | average accuracy: 79.3 -> 81.0 | Helped |
| Reduce German NC training data from 8,000 to 30 examples (ablation) | Federated prompt tuning and local monolingual fine-tuning · German News Classification | accuracy | Mixed |
| Apply federated prompt tuning rather than local fine-tuning across languages with greater distance from the pre-trained language (ablation) | XLM-RoBERTa base · News Classification and XNLI | accuracy | Helped |
Surprising findings
- Federated prompt tuning on some languages outperforms the centralized approach, which the authors attribute to implicit regularization.
Limitations
- No added privacy protection (differential privacy or secure aggregation) against attacks such as gradient inversion.
- Evaluated only on a base-sized model (XLM-RoBERTa-base) and classification/NLI tasks; future scale study planned.
- Some results show PE_FL underperforming centralized or LoRA variants on specific languages (e.g., Hausa, Yoruba on MasakhaNEWS).
Experimental setup
Datasets: XGLUE News Classification XNLI MasakhaNEWS UN Corpus
Benchmarks: XGLUE NC XNLI MasakhaNEWS
Metrics: accuracy communication cost (MB/GB) trainable parameter fraction
Baselines: Monolingual fine-tuning Centralized fine-tuning Federated full fine-tuning Federated LoRA PE_Monolingual PE_Centralized
Builds on: FedAvg prompt tuning LoRA XLM-RoBERTa
Closest papers by meaning
- Ferret: Federated Full-Parameter Tuning at Scale for Large Language Models (ICML 2025 · similarity 0.89)
- Federated Full-Parameter Tuning of Billion-Sized Language Models with Communication Cost under 18 Kilobytes (ICML 2024 · similarity 0.89)
- FedBPT: Efficient Federated Black-box Prompt Tuning for Large Language Models (ICML 2024 · similarity 0.89)
- FlowerTune: A Cross-Domain Benchmark for Federated Fine-Tuning of Large Language Models (NeurIPS 2025 · similarity 0.89)
- When Scaling Meets LLM Finetuning: The Effect of Data, Model and Finetuning Method (ICLR 2024 · similarity 0.89)
- FLoRA: Federated Fine-Tuning Large Language Models with Heterogeneous Low-Rank Adaptations (NeurIPS 2024 · similarity 0.88)
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