The preeminence of English as the lingua franca in global science has led to English-dominant publication practices, even in non-English-speaking countries. We examine the complex dynamics of language use in scientific publications in China, a major contributor to global scientific output, and the tensions between English and the native language. By analyzing 2,209,987 multilingual publications from 183,457 projects funded by the National Natural Science Foundation of China, we reveal a strong preference for English as the publication language in China, with 66.2% of publications in English versus 33.8% in Chinese. Key projects and natural sciences and engineering projects favor English more; regional projects and social sciences projects use Chinese more. However, English has a growing prevalence over the years across all research fields, project types, and publication venues. There is a negative correlation between the shares of English usage in journals and conference proceedings. We find only a minor overlap between English and Chinese-language publications, indicating unique contributions rather than repetitive content. However, Chinese-language publications are more likely to be similar to English-language publications. For highly similar cross-language publication pairs, the Chinese version tends to be published earlier. The findings underscore the risk of underestimating China's scientific output by only counting English-language publications. We highlight the importance of creating a comprehensive multilingual database and the significant role of non-English-language research in global scientific discourse.Keywords: multilingual publishing; scientific communication; language policy; academic multilingualism; bibliometrics; quantitative analysis.