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arxiv: 2512.01512 · v2 · submitted 2025-12-01 · 💻 cs.CL

MCAT: Scaling Many-to-Many Speech-to-Text Translation with MLLMs to 70 Languages

Pith reviewed 2026-05-17 03:10 UTC · model grok-4.3

classification 💻 cs.CL
keywords speech-to-text translationmany-to-many translationmultimodal large language modelscurriculum learningspeech adapterlanguage scalingFLEURS benchmark
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The pith

MCAT scales MLLM speech translation to mutual support among 70 languages while compressing audio to 30 tokens for faster inference.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper seeks to expand multimodal large language models beyond English-centric data limits and slow processing of long speech sequences in speech-to-text translation. It presents the MCAT framework that applies curriculum learning plus data balancing to reach 70-language coverage with many-to-many capabilities. A redesigned speech adapter shrinks input sequences to just 30 tokens. Tests on 9B and 27B models show gains over prior end-to-end systems on the FLEURS benchmark across all 70 by 69 directions together with quicker inference.

Core claim

Curriculum learning combined with data balancing extends MLLM many-to-many speech-to-text translation to 70 languages, and an optimized adapter reduces speech sequences to 30 tokens, yielding results that surpass state-of-the-art end-to-end models on FLEURS in 70x69 directions while raising inference efficiency.

What carries the argument

The MCAT framework, built on curriculum learning and data balancing for language scaling together with an optimized speech adapter that shortens speech token sequences to 30.

If this is right

  • Surpasses existing end-to-end models across every 70x69 translation direction on FLEURS.
  • Raises inference speed by shortening speech token sequences.
  • Maintains performance gains on both 9B and 27B scale MLLMs.
  • Enables mutual translation support among the full set of 70 languages.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The token-compression approach may transfer to other speech or audio multimodal tasks.
  • Wider language coverage could support translation tools for previously underserved regions.
  • Open release of the models invites direct testing on additional low-resource language pairs.

Load-bearing premise

Curriculum learning and data balancing can scale MLLM translation to 70 languages without quality loss, and the adapter's reduction to 30 tokens keeps all needed speech information intact.

What would settle it

Direct side-by-side FLEURS evaluation in which MCAT fails to beat prior end-to-end models on non-English-centric pairs or shows no inference speedup with the 30-token adapter.

Figures

Figures reproduced from arXiv: 2512.01512 by Bing Qin, Bo Yang, Kaiyuan Liu, Keqi Deng, Ming Liu, Xie Chen, Yang Xiang, Yaowei Wang, Yexing Du, Youcheng Pan.

Figure 1
Figure 1. Figure 1: Comparison of S2TT MLLMs. (a) compresses speech to 750 tokens, has limited language support, and directly generates translated text; (b) gen￾erates transcriptions and translations in a single end-to-end pass, compressing speech to 30 tokens, supporting 70 languages. <|eng|><|cmn|> indicates transcribing English and translating it into Chinese. vantages in simplifying the model architecture and mitigating e… view at source ↗
Figure 2
Figure 2. Figure 2: Key Features: (a) Multilingual Support; (b) Low-Resource Require￾ment; (c) Lightweight Training; (d) High-Efficiency Inference. Based on the above design, Multilingual Cost-effective Accelerated Speech-to-Text Translator (MCAT) models ex￾hibit four key features shown in [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: The Architecture of MCAT Model. Our MLLM compresses the input audio into 30 tokens, supporting a total of 70 languages. c) MLP for Dimension Alignment: The MLP maps the compressed features into the LLM’s dimension Dllm: Zmlp = MLP(Zp), Zmlp ∈ R N×K/S×Dllm (5) where Zmlp represents the aligned speech feature embeddings, ready for concatenation. 4) Text Embedding: Given the instruction text t, the cor￾respon… view at source ↗
Figure 4
Figure 4. Figure 4: COMET Scores for the English→69 Translation Directions on the FLEURS Dataset. The blue bars denote stronger translation performance for the MCAT-Large model in a total of 55 directions. C. Eng→X S2TT on FLEURS Table IV presents a comprehensive comparison of the per￾formance of various end-to-end translation models across 27 target language directions originating from English, evaluated using the COMET metr… view at source ↗
Figure 5
Figure 5. Figure 5: COMET Scores Across 70 × 70 Translation Directions. For cases like eng → eng, no score is calculated, and smoothing was applied in the figure. TABLE VIII COMET SCORES STATISTICS ON THE FLEURS DATASET. Models x ≥90 90> x ≥80 80> x ≥70 x <70 Total MCAT-Small-9B 0 399 265 92 28 × 27 MCAT-Large-27B 6 2197 1834 793 70 × 69 SeamlessM4T-V2-Large 0 215 2719 1896 70 × 69 D. COMET Score Across 70 Languages 1) Compar… view at source ↗
Figure 6
Figure 6. Figure 6: Average Performance Across 70 Languages. 4) Asymmetry in Low-Resource Language: As shown in [PITH_FULL_IMAGE:figures/full_fig_p008_6.png] view at source ↗
read the original abstract

Multimodal Large Language Models (MLLMs) have achieved great success in Speech-to-Text Translation (S2TT) tasks. However, current research is constrained by two key challenges: language coverage and efficiency. Most of the popular S2TT datasets are substantially English-centric, which restricts the scaling-up of MLLMs' many-to-many translation capabilities. Moreover, the inference speed of MLLMs degrades dramatically when the speech is converted into long sequences (e.g., 750 tokens). To address these limitations, we propose a Multilingual Cost-effective Accelerated Speech-to-Text Translator (MCAT) framework, which includes two innovations. First, a language scaling method that leverages curriculum learning and a data balancing strategy is introduced to extend the language coverage supported by MLLMs to 70 languages and achieve mutual translation among these languages. Second, an optimized speech adapter module is designed to reduce the length of the speech sequence to only 30 tokens. Extensive experiments were conducted on MLLMs of different scales (9B and 27B). The experimental results demonstrate that MCAT not only surpasses state-of-the-art end-to-end models on the FLEURS dataset across 70x69 directions but also enhances inference efficiency. The code and models are released at https://github.com/yxduir/m2m-70.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper introduces the MCAT framework to scale many-to-many speech-to-text translation (S2TT) with multimodal LLMs to 70 languages. It proposes two main innovations: (1) a language scaling approach using curriculum learning and data balancing to enable mutual translation among 70 languages, and (2) an optimized speech adapter that compresses input speech sequences to only 30 tokens. Experiments on 9B and 27B MLLMs report surpassing prior end-to-end SOTA models on the FLEURS benchmark across 70×69 directions while also improving inference efficiency; code and models are released.

Significance. If the empirical claims hold after verification, the work would be a meaningful contribution to multilingual S2TT by simultaneously tackling limited language coverage (beyond English-centric datasets) and the quadratic inference cost of long speech token sequences in MLLMs. Demonstrating scalable many-to-many performance with a 30-token adapter on both 9B and 27B models, together with public code release, would provide a practical baseline for future efficiency-focused multilingual speech translation research.

major comments (2)
  1. [§4.2] §4.2 (Optimized Speech Adapter): The central efficiency claim rests on the assertion that the adapter compresses speech to 30 tokens without systematic information loss. No ablation is reported that directly compares BLEU or other metrics for 30-token vs. longer sequences (e.g., 100+ tokens) on FLEURS low-resource language subsets; without this, it remains unclear whether the reported average gains mask quality degradation in specific directions.
  2. [§5] §5 (Experiments): The claim that MCAT surpasses SOTA end-to-end models across all 70×69 directions is load-bearing for the paper’s contribution, yet the manuscript provides only aggregate results without per-direction breakdowns, statistical significance tests, or detailed baseline hyper-parameter matching. This weakens the strength of the cross-lingual scaling conclusion.
minor comments (2)
  1. [Abstract] The abstract and §1 could more explicitly define the 70×69 direction count (e.g., whether self-translations are excluded) to avoid ambiguity.
  2. [§5] Figure captions and tables in the experimental section would benefit from clearer indication of which results are zero-shot vs. fine-tuned and which languages are low-resource.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive and detailed feedback. We address each major comment below and indicate the changes we will make in the revised manuscript to strengthen the presentation of our results.

read point-by-point responses
  1. Referee: [§4.2] §4.2 (Optimized Speech Adapter): The central efficiency claim rests on the assertion that the adapter compresses speech to 30 tokens without systematic information loss. No ablation is reported that directly compares BLEU or other metrics for 30-token vs. longer sequences (e.g., 100+ tokens) on FLEURS low-resource language subsets; without this, it remains unclear whether the reported average gains mask quality degradation in specific directions.

    Authors: We acknowledge that a direct ablation of token length on low-resource subsets would provide stronger support for the claim of no systematic information loss. The 30-token length was selected based on internal trade-off experiments balancing compression and quality, but these were not reported in detail. In the revision we will add an ablation table comparing 30-, 60-, and 100-token variants on selected low-resource FLEURS directions to demonstrate that performance remains competitive at 30 tokens. revision: yes

  2. Referee: [§5] §5 (Experiments): The claim that MCAT surpasses SOTA end-to-end models across all 70×69 directions is load-bearing for the paper’s contribution, yet the manuscript provides only aggregate results without per-direction breakdowns, statistical significance tests, or detailed baseline hyper-parameter matching. This weakens the strength of the cross-lingual scaling conclusion.

    Authors: We agree that aggregate results alone limit the ability to assess consistency across directions. The original submission reported averages due to space constraints. We will expand the experimental section to include (i) per-direction BLEU scores for a representative sample of directions, (ii) statistical significance tests on the main comparisons, and (iii) explicit clarification of baseline hyper-parameter settings and any adaptations made for fair comparison. revision: yes

Circularity Check

0 steps flagged

No significant circularity; empirical claims rest on external benchmarks

full rationale

The paper describes an empirical framework: curriculum learning plus data balancing to scale to 70 languages, plus an optimized adapter compressing speech to 30 tokens. Performance is shown via direct comparison to external SOTA end-to-end models on the FLEURS dataset across 70x69 directions. No equations, first-principles derivations, or predictions appear that reduce by construction to fitted parameters or self-definitions. No load-bearing self-citations or uniqueness theorems are invoked. The central results are falsifiable against independent benchmarks and therefore self-contained.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on standard assumptions in multimodal ML training and the representativeness of FLEURS for evaluating 70-language performance; no new entities are postulated and free parameters appear limited to typical training choices.

axioms (2)
  • domain assumption Curriculum learning and data balancing can effectively extend MLLM translation capabilities across a large set of languages without major quality loss
    Invoked in the language scaling method description.
  • domain assumption Compressing speech sequences to 30 tokens preserves sufficient information for high-quality translation
    Central to the optimized speech adapter design.

pith-pipeline@v0.9.0 · 5571 in / 1529 out tokens · 37511 ms · 2026-05-17T03:10:36.429642+00:00 · methodology

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Reference graph

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    9 JOURNAL OF LATEX CLASS FILES, VOL. 18, NO. 9, SEPTEMBER 2020 11 APPENDIX A. Language Coverage The MLLM’s S2TT capability is contingent upon the upper bound of the underlying LLM’s MT performance. Conse- quently, the MT capability of the base model directly deter- mines the ceiling of our translation quality and guides our final selection of supported la...