What makes a word hard to learn? Modeling L1 influence on English vocabulary difficulty

TL;DR

This study models English vocabulary difficulty for learners with Spanish, German, or Chinese as their native language, highlighting the role of familiarity, orthographic transfer, and surface features in predicting difficulty.

Contribution

It introduces an interpretable, L1-specific modeling approach for vocabulary difficulty, incorporating cross-linguistic transfer and feature importance analysis.

Findings

Familiarity is the most important feature across all L1 groups.

Orthographic transfer influences Spanish and German learners' difficulty predictions.

Chinese learners' difficulty is mainly shaped by familiarity and surface features.

Abstract

What makes a word difficult to learn, and how does the difficulty depend on the learner's native language? We computationally model vocabulary difficulty for English learners whose first language is Spanish, German, or Chinese with gradient-boosted models trained on features related to a word's familiarity (e.g., frequency), meaning, surface form, and cross-linguistic transfer. Using Shapley values, we determine the importance of each feature group. Word familiarity is the dominant feature group shared by all three languages. However, predictions for Spanish- and German-speaking learners rely additionally on orthographic transfer. This transfer mechanism is unavailable to Chinese learners, whose difficulty is shaped by a combination of familiarity and surface features alone. Our models provide interpretable, L1-tailored difficulty estimates that can be used to design vocabulary curricula.