In the Arabic-speaking world, it is a primary reference for scholars. However, because it is an enormous multi-volume work (often 20+ volumes in Arabic), translating it into English is a monumental task that has yet to be finished by any major academic or religious publisher.
If you want, I can:
Below is a short, informative essay on the significance of Al-Majmu' , its contents, and the availability of English translations or PDFs. kitab al-majmu english pdf
Ensure you are looking for the correct version, as these books share a name but represent entirely different branches of Islamic thought. In the Arabic-speaking world, it is a primary