Both the Shiva Purana and the Linga Purana are books on Lord Shiva. I have read Shiva Purana. Can somebody please explain what is extra or differently told in the Linga Purana? Also, if possible please add a link of verse by verse English translation of the Linga Purana.
The difference between the Shiva Purana and the Linga Purana is analogous to the difference between the Vishnu Purana and the Srimad Bhagavatam; the Vishnu Purana is an older work, focusing on Vishnu in general rather than Krishna in particular, whereas the Srimad Bhagavatam puts more emphasis on Krishna, although it still recounts Vishnu stories unconnected to Krishna. Similarly, the Shiva Purana is a work dealing with Shiva in general. It was composed by the sage Parashara, Vyasa's father, and it was condensed by Vyasa into a much shorter work, with some or all of the removed parts put into the Vayu Purana. The Linga Purana, on the other hand, was composed later and puts more emphasis on Shiva's Linga form, how to worship a Shiva Linga, etc., although it still recounts stories of Shiva unconnected to the Shiva Linga.
As far as I know, the only unabridged translation of the Linga Purana is the two-volume translation published by Motilal Banarsidass. Here are links to the two volumes in PDF format:
Volume 1 is on DSpace, the digital repository of the West Bengal Public Library Network. I found Volume 2 on the Digital Library of India, and then I downloaded it as a PDF file using the program DLI downloader, and I uploaded it to Google Drive.
One note of caution: it's believed that the Linga Purana contains a lot of interpolations, because other ancient works which quote the Linga Purana quote things that are not in the actual text we have and don't quote things which are in the text we have. This leads some people to believe that the Linga Purana we have today is a complete interpolation, but it could just be that it contains so many interpolations that the overlap between content quoted in other works and content preserved is negligible. See page 93 of this book for details.