A Universal Vibe? Finding and Controlling Language-Agnostic Informal Register with SAEs

Title:A Universal Vibe? Finding and Controlling Language-Agnostic Informal Register with SAEs

Abstract:While multilingual language models successfully transfer factual and syntactic knowledge across languages, it remains unclear whether they process culture-specific pragmatic registers, such as slang, as isolated language-specific memorizations or as unified, abstract concepts. We study this by probing the internal representations of Gemma-2-9B-IT using Sparse Autoencoders (SAEs) across three typologically diverse source languages: English, Hebrew, and Russian. To definitively isolate pragmatic register processing from trivial lexical sensitivity, we introduce a novel dataset in which every target term is polysemous, appearing in both literal and informal contexts. We find that while much of the informal-register signal is distributed across language-specific features, a small but highly robust cross-linguistic core consistently emerges. This shared core forms a geometrically coherent ``informal register subspace'' that sharpens in the model's deeper layers. Crucially, these shared representations are not merely correlational: activation steering with these features causally shifts output formality across all source languages and transfers zero-shot to six unseen languages spanning diverse language families and scripts. Together, these results provide the first mechanistic evidence that multilingual LLMs internalize informal register not just as surface-level heuristics, but as a portable, language-agnostic pragmatic abstraction.

Camera-ready version. Accepted at EMNLP 2026

Computation and Language (cs.CL)

arXiv:2603.26236 [cs.CL]

(or arXiv:2603.26236v2 [cs.CL] for this version)

https://doi.org/10.48550/arXiv.2603.26236 Focus to learn more arXiv-issued DOI via DataCite

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