Representation Learning Enables Language Identification in Zero- and Few-Shot Settings

Language Identification (LID) is a key component of multilingual NLP pipelines and multilingual corpus construction. LID errors can create spurious text–language associations, harming downstream model quality, especially for low-resource languages and fine-grained taxonomies involving closely related languages and dialects. We propose LIBE, a representation-based approach that embeds input texts and natural-language descriptions into a shared semantic space with a bi-encoder, enabling LID via similarity search. This formulation supports data-efficient learning and the addition of new languages through their descriptions. To improve discrimination in ambiguous or low-resource cases, we also introduce an optional cross-encoder re-ranking stage. Across multiple benchmarks, LIBE achieves competitive performance with strong LID systems when initialized from pretrained multilingual encoders, while requiring substantially less task-specific LID supervision in several adaptation settings. The hybrid bi-encoder– cross-encoder formulation further improves robustness in challenging open-set scenarios, achieving up to 90% F1 with as few as five labeled examples. Code and data are available at https://github.com/cafoscari-nlp/LIBE.