Multilingual LLMs share a core interlingual subspace with language-specific fragments

Wilie et al. study Aya Expanse 8B, Llama-3.1-8B and Gemma-2-9B with a kNN-based Interlingual Local Overlap (ILO) score plus t-SNE of hidden states [wilie-etal-2025-high-dimensional-interlingual-representations] Representations organize as a partially-shared core interlingual region (translation-equivalent inputs share local neighborhoods) surrounded by fragmented language-specific components that do not transfer [wilie-etal-2025-high-dimensional-interlingual-representations] Overlap varies systematically by resource level and linguistic family, with graph "bridge"/"reachability" metrics showing which languages connect the core to peripheral fragments [wilie-etal-2025-high-dimensional-interlingual-representations] The alignment is causally load-bearing: ILO overlap is preserved or disrupted depending on which layers are frozen during single-language fine-tuning [wilie-etal-2025-high-dimensional-interlingual-representations]