SIGNALAI·Jun 18, 2026, 4:00 AMSignal55Medium term

Dango: A Strictly L1-Only Large Language Model for Studying Second Language Acquisition

Source: arXiv cs.CL

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Dango: A Strictly L1-Only Large Language Model for Studying Second Language Acquisition

arXiv:2606.19170v1 Announce Type: new Abstract: We introduce Dango, a 1.8B-parameter large language model designed for controlled studies of L1-to-L2 (Japanese-to-English) transfer in second language acquisition (SLA). While previous studies have explored SLA in language models, they have predominantly relied on smaller or non-decoder models, limiting their ability to generate open-ended text and reducing their suitability as practical L2 simulators. We identify a key challenge when scaling models to this size: L2 contamination within the "monolingual" pretraining corpus used for L1 acquisitio

Why this matters
Why now

The development of Dango reflects the accelerating push to apply specialized large language models to complex cognitive tasks like second language acquisition, moving beyond general-purpose applications.

Why it’s important

This research provides a more robust tool for studying human language learning, offering insights into L1-L2 transfer that could inform more effective language education and AI systems.

What changes

The introduction of L1-only LLMs like Dango allows for more controlled experimental conditions in SLA research, potentially refining our understanding of language acquisition mechanisms in both humans and machines.

Winners
  • · AI researchers
  • · Linguists
  • · EdTech companies
  • · Language learning platforms
Losers
  • · Traditional language acquisition research methods
  • · Less specialized AI models for SLA
Second-order effects
Direct

More sophisticated and scientifically grounded AI tools emerge for language education and analysis.

Second

Understanding of L1-L2 transfer mechanisms could lead to more efficient human language learning strategies and curriculum development.

Third

The methodology could be extended to study other cognitive biases or learning processes in AI, bridging neuroscience and AI development.

Editorial confidence: 85 / 100 · Structural impact: 40 / 100
Original report

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