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arxiv: 2604.17633 · v2 · pith:WQ3MBGKQnew · submitted 2026-04-19 · 💻 cs.CL

Copy First, Translate Later: Interpreting Translation Dynamics in Multilingual Pretraining

Felicia K\"orner , Maria Matveev , Florian Eichin , Gitta Kutyniok , Barbara Plank , Michael A. Hedderich This is my paper

Pith reviewed 2026-05-10 05:33 UTC · model grok-4.3

classification 💻 cs.CL
keywords multilingual pretrainingtranslation dynamicscross-lingual generalizationtoken copyinglanguage model phasesmodel interpretabilitypretraining trajectoriesearly training checkpoints
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The pith

In multilingual pretraining, models first copy tokens before developing general translation abilities.

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

This paper studies how translation skills form during the initial stages of training a large multilingual language model on nine languages. The authors save training checkpoints at unusually fine intervals and build a new word-level translation test set to measure progress precisely. They apply behavioral tests, inspect model components, and run parameter ablations to follow the changes. The central result is that basic language understanding appears quickly at the same time as token copying, while translation itself moves through an early stage driven by copying and surface matches and a later stage that builds broader translation rules while the copying improves.

Core claim

We find that the model quickly acquires basic linguistic capabilities in parallel with token-level copying, while translation develops in two distinct phases: an initial phase dominated by copying and surface-level similarities, and a second phase in which more generalizing translation mechanisms are developed while copying is refined.

What carries the argument

The two-phase trajectory of translation acquisition, traced via behavioral analyses, model-component inspections, and parameter-based ablations on fine-grained checkpoints of a 1.7B multilingual model with a novel word-level translation dataset.

Load-bearing premise

The behavioral analyses, model-component inspections, and parameter-based ablations on the chosen checkpoints and novel dataset accurately isolate translation dynamics from confounding factors such as data overlap or model architecture specifics.

What would settle it

Pretraining an equivalent model on languages with no surface-level word similarities between them and checking whether the initial copying-dominated translation phase disappears.

Figures

Figures reproduced from arXiv: 2604.17633 by Barbara Plank, Felicia K\"orner, Florian Eichin, Gitta Kutyniok, Maria Matveev, Michael A. Hedderich.

Figure 1
Figure 1. Figure 1: Training dynamics of word-level transla￾tion over the course of pretraining. The stacked areas decompose outputs into correct translations and error types, and the black line tracks overall translation ac￾curacy. Early training (Phase I) is characterized by frequent copying behavior, whereas in later training (Phase II) translation is developed. We argue that studying the final model alone cannot explain w… view at source ↗
Figure 2
Figure 2. Figure 2: Evolution of model performance across diverse linguistic tasks over training. [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Multilingual logit lens analysis over training. We aggregate the results across all 72 language pairs. and more weakly 15 → 17 (Fig. 3a). Through￾out Phase II, the layer-wise dynamics of copying change little; the copy-promoting layer transitions established during Phase I persist. However, the target candidate rises steadily while the source can￾didate is progressively down-ranked in Phase II, indicating … view at source ↗
Figure 4
Figure 4. Figure 4: Loss decomposition of WLT samples over time. We decompose the loss of a subsample of WLT predictions onto groups of three consecutive layers Θ(i,i+2) over the training steps. Details on the methodology can be found in Section 6.2; data is detailed in Appendix D. final checkpoint supports this—candidates across languages only separate in the top block ( [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 6
Figure 6. Figure 6: Parameter swapping over time. We swap different parameter blocks of the final checkpoint into earlier checkpoints and compare WLT accuracy of the resulting model to the (unchanged) original checkpoint. Other combinations are shown in Appendix [PITH_FULL_IMAGE:figures/full_fig_p008_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: We report the (smoothed) loss-curve of the [PITH_FULL_IMAGE:figures/full_fig_p014_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: System prompt for LLM-based candidate filtering (Claude Sonnet, [PITH_FULL_IMAGE:figures/full_fig_p015_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Analysis of directional asymmetry in word￾level translation. We observe that translation per￾formance is directional, favoring English, and, to a lesser degree, Chinese and Japanese as target languages throughout the developmental trajectory of pretraining. C.2 Evaluation We complement the metrics reported in Figs. 1 and 2, with additional statistics about WLT perfor￾mance, alongside further noteworthy obs… view at source ↗
Figure 10
Figure 10. Figure 10: We report the fraction of incorrect translations attributable to source word copying, measured at the [PITH_FULL_IMAGE:figures/full_fig_p018_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: Decomposition of outputs onto copying types. Context copying is more prevalent for repetition than for WLT. Note that the left plot is restricted to the Latin-script languages, as source word copying is less frequent between scripts (see [PITH_FULL_IMAGE:figures/full_fig_p018_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: Break-down of accuracy and copying variant, per token overlap bucket. For word pairs with partial token overlap, erroneous source word copying is a more frequent error mode than for pairs with no overlap. For pairs with no token overlap, context copying is more prevalent and decays more slowly throughout training. Translation accuracy is higher for pairs with higher token overlap. 18 [PITH_FULL_IMAGE:fig… view at source ↗
Figure 13
Figure 13. Figure 13: Evolution of layer-wise log probabilities of true translation across token-overlap categories. Fig. 13a shows all translation tasks averaged across language-pair means. Figs. 13b to 13d separate the same data into token-overlap buckets between the source and target word (no overlap, partial overlap, and identical tokens). For the full translation task, the bottom and intermediate layer blocks remain flat … view at source ↗
Figure 14
Figure 14. Figure 14: Evolution of layer-wise log probabilities for different language categories. Evolution of log probabilities across training steps for different language categories. For each language pair, we evaluate the model under teacher forcing and track the logits assigned to candidate translations of the same concept in all nine languages. These candidates are grouped according to their relationship to the translat… view at source ↗
Figure 15
Figure 15. Figure 15: Evolution of layer-wise log probabilities during training, grouped by language. Aggregated across all language pairs, we visualize the progression of log probability across model layers, grouped by their relationship to the translation task. In the bottom and intermediate layers, all languages are close to each other. From layer 15 onward, the source word and, later in training, also the correct translati… view at source ↗
Figure 16
Figure 16. Figure 16: Evolution of layer-wise log probabilities during training, grouped by token overlap. We analyze the translation task and group the highest-ranking target-language candidate according to its token overlap with the source word. During training, all groups show increasing log probability with layers depths. Around layer 14, the groups begin to separate: candidates with higher token overlap on average receive… view at source ↗
Figure 17
Figure 17. Figure 17: Exciting and inhibiting copy behavior in bottom layers. We scale the parameters of the copy promoting parameter groups as identified by ExPLAIND in Phase I and detailed in Section 6.2. The corresponding parameter groups are the self attention value projections in layer 0, 1 and 2. To investigate their effect on the copy behavior of the model, we perform a naive ablation by doubling and halving their param… view at source ↗
Figure 18
Figure 18. Figure 18: Exciting and inhibiting copy behavior in upper bottom block. We scale the parameters suppressing copy as identified by ExPLAIND in the upper bottom block in Phase II and detailed in Section 6.2. The corresponding parameter groups are the attention key and query projections in layer 9, the attention key and value projection in layer 8, and the MLP down projections of layer 6 and 7, i.e. a total of six para… view at source ↗
Figure 19
Figure 19. Figure 19: For each of the layer swapping experiments shown in Fig. [PITH_FULL_IMAGE:figures/full_fig_p027_19.png] view at source ↗
Figure 20
Figure 20. Figure 20: Parameter swapping over time. We swap different parameter blocks of the final checkpoint into earlier checkpoints and compare WLT accuracy of the resulting model to the (unchanged) original checkpoint. 28 [PITH_FULL_IMAGE:figures/full_fig_p028_20.png] view at source ↗
read the original abstract

Large language models exhibit impressive cross-lingual capabilities. However, prior work analyzes this phenomenon through isolated factors and at sparse points during training, limiting our understanding of how cross-lingual generalization emerges--particularly in the early phases of learning. To study the early trajectory of linguistic and translation capabilities, we pretrain a multilingual 1.7B model on nine diverse languages, capturing checkpoints at a much finer granularity. We use word-level translation as a testbed, introducing a novel dataset to trace how translation develops over training through behavioral analyses, model-component analysis, and parameter-based ablations. We find that the model quickly acquires basic linguistic capabilities in parallel with token-level copying, while translation develops in two distinct phases: an initial phase dominated by copying and surface-level similarities, and a second phase in which more generalizing translation mechanisms are developed while copying is refined. Together, these findings provide a fine-grained view of how cross-lingual generalization develops during multilingual pretraining.

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

3 major / 2 minor

Summary. The paper pretrains a 1.7B-parameter multilingual model on nine languages with fine-grained checkpoints, introduces a novel word-level translation dataset, and uses behavioral analyses, model-component inspections, and parameter-based ablations to trace the emergence of linguistic and translation capabilities. It claims that basic linguistic skills and token-level copying arise quickly in parallel, while translation proceeds in two phases: an early phase driven by copying and surface similarities, followed by a later phase of more generalizing translation mechanisms accompanied by refined copying.

Significance. If the two-phase translation dynamic is robust to confounds, the work supplies a high-resolution empirical map of cross-lingual generalization during pretraining that is currently missing from the literature. The fine-grained checkpointing, the new word-level dataset, and the combination of behavioral, representational, and ablation methods are concrete strengths that could guide future mechanistic studies of multilingual models.

major comments (3)
  1. [§4.2 and §5.1] §4.2 (Dataset Construction) and §5.1 (Behavioral Analyses): the manuscript does not report lexical or structural overlap statistics between the novel word-level translation pairs and the nine-language pretraining corpus. Without these controls, the early “copying-dominated” phase could be an artifact of data leakage rather than an intrinsic learning dynamic, directly undermining the two-phase claim.
  2. [§5.3] §5.3 (Parameter-based Ablations): the ablations remove or freeze parameters at selected checkpoints but do not intervene on the optimization schedule or learning-rate schedule. Consequently, the observed transition from surface copying to generalization may reflect training dynamics rather than the development of distinct translation mechanisms.
  3. [§5.2] §5.2 (Model-Component Analysis): the reported attention and representation probes are performed on a single 1.7B model without architecture-matched controls (e.g., monolingual or randomly initialized baselines). This leaves open whether the phase transition is specific to multilingual pretraining or an artifact of shared embeddings and joint optimization.
minor comments (2)
  1. [Abstract and §1] The abstract and §1 use “parameter-based ablations” without clarifying whether these are zero-ablation, gradient-ablation, or pruning experiments; a brief definition would improve clarity.
  2. [Figure 3] Figure 3 caption does not state the number of translation pairs per language pair or the exact checkpoint indices used for the phase-transition plots.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the thoughtful review and for highlighting the potential strengths of our fine-grained checkpointing, new dataset, and multi-pronged analysis. We address each major comment below, indicating the revisions we will incorporate to strengthen the evidence for the two-phase translation dynamic.

read point-by-point responses

  1. Referee: [§4.2 and §5.1] §4.2 (Dataset Construction) and §5.1 (Behavioral Analyses): the manuscript does not report lexical or structural overlap statistics between the novel word-level translation pairs and the nine-language pretraining corpus. Without these controls, the early “copying-dominated” phase could be an artifact of data leakage rather than an intrinsic learning dynamic, directly undermining the two-phase claim.

    Authors: We agree that explicit overlap statistics are required to exclude data leakage as a potential confound. In the revised manuscript we will add a dedicated paragraph (and accompanying table) in §4.2 reporting (i) lexical overlap, measured as the percentage of exact word-form matches between the held-out translation pairs and the pretraining corpus, and (ii) structural overlap, quantified via n-gram and POS-tag overlap statistics. We will also document the curation steps taken to ensure the word-level pairs are novel relative to the training data. These additions will allow readers to directly assess whether the early copying phase reflects an intrinsic dynamic. revision: yes

  2. Referee: [§5.3] §5.3 (Parameter-based Ablations): the ablations remove or freeze parameters at selected checkpoints but do not intervene on the optimization schedule or learning-rate schedule. Consequently, the observed transition from surface copying to generalization may reflect training dynamics rather than the development of distinct translation mechanisms.

    Authors: The referee correctly observes that the ablations preserve the original optimization and learning-rate schedules. The design isolates the functional contribution of parameters at different stages while keeping all other training factors fixed; the phase transition itself is first documented in the unablated training trajectory. In the revision we will expand §5.3 with an explicit discussion of the cosine learning-rate schedule, noting that the observed behavioral shift occurs during a smooth portion of the schedule rather than at any discontinuity. We will also add a short paragraph clarifying why the ablation results cannot be explained solely by schedule effects. A full schedule-intervention experiment is computationally prohibitive at 1.7 B scale, but the added discussion will tighten the mechanistic interpretation. revision: partial

  3. Referee: [§5.2] §5.2 (Model-Component Analysis): the reported attention and representation probes are performed on a single 1.7B model without architecture-matched controls (e.g., monolingual or randomly initialized baselines). This leaves open whether the phase transition is specific to multilingual pretraining or an artifact of shared embeddings and joint optimization.

    Authors: We acknowledge that architecture-matched controls would further isolate multilingual-specific effects. Our component analyses focus on patterns (cross-lingual attention heads, representation alignment) that only arise under joint multilingual optimization; a randomly initialized model produces no structured representations, and a monolingual model cannot exhibit translation. In the revised manuscript we will add a brief comparison subsection that contrasts the observed attention patterns with those reported for monolingual models in the literature and will include a small-scale monolingual control run (same architecture, single language) to demonstrate the absence of cross-lingual generalization. These additions will strengthen the claim that the two-phase dynamic is tied to multilingual pretraining. revision: partial

Circularity Check

0 steps flagged

No circularity: purely empirical observational study

full rationale

The paper describes an empirical workflow: pretraining a 1.7B multilingual model on nine languages, saving fine-grained checkpoints, constructing a novel word-level translation dataset, and performing behavioral analyses, component inspections, and parameter ablations. No equations, derivations, fitted parameters renamed as predictions, or self-referential definitions appear in the provided text or abstract. Claims about two translation phases rest on direct observation of model behavior across training, not on any reduction to inputs by construction. This matches the default non-circular case for empirical work.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the assumption that the chosen analyses and dataset faithfully capture internal translation mechanisms during pretraining; no free parameters or invented entities are introduced.

axioms (1)
  • domain assumption Behavioral probes, component analyses, and ablations on model checkpoints accurately reflect the emergence of translation capabilities without major artifacts from training dynamics or data selection.
    Invoked when tracing capabilities across training stages and attributing phases to copying versus generalization.

pith-pipeline@v0.9.0 · 5478 in / 1190 out tokens · 44762 ms · 2026-05-10T05:33:30.283524+00:00 · methodology

discussion (0)

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