TRANS.TBL was a crude way to support (or at least record) long filenames on ISO 9660 CD-ROMs. The original ISO 9660 standard was limited to DOS "8.3"-style filenames. TRANS.TBL became obsolete as other extensions, mainly Rock Ridge and Joliet, became widely supported.
Authoritative information about TRANS.TBL is hard to find, but it's easy to figure out the basics of it. A text file named "TRANS.TBL" or, apparently, "00_TRANS.TBL", is placed in every directory. It contains a list of the other files and subdirectories in that directory, and their corresponding long filenames.