Users' cross-lingual queries to a digital library system might be short and not included in a common translation dictionary (unknown terms). In this paper, we investigate the feasibility of exploiting the Web as the corpus source to translate unknown query terms for cross-language information retrieval (CLIR) in digital libraries. We propose a Web-based term translation approach to determine effective translations for unknown query terms by mining bilingual search-result pages obtained from a real Web search engine. This approach can enhance the construction of a domain-specific bilingual lexicon and benefit CLIR services in a digital library that only has monolingual document collections. Very promising results have been obtained in generating effective translation equivalents for many unknown terms, including proper nouns, technical terms and Web query terms.