Given an old ClarisWorks 4 Japanese document and a working copy of ClarisWorks 4 Japanese Edition, in theory you can just export it to Word, and the Japanese text will be translated correctly. If you are running on an Intel-based Mac, this won’t work. Actually, unless you can do a clean reinstall of CW4JP under a copy of Classic that has the Japanese language kit installed, it might not work at all.
AppleWorks 6, however, which is still available in stores and runs nicely under Rosetta, will. At least, with a little help.
If your AppleWorks install is damaged or incomplete, it won’t be able to open CW4JP docs; you’ll have to reinstall. The English version bundled with PowerPC-based Macs for a long time works just fine, so if you’ve got one, you don’t need to buy the retail package. I use the copy that came with my PowerBook, which was automatically transferred to my new MacBook.
Note that DataViz MacLinkPlus, for all its virtues, hasn’t the slightest idea what to do with Japanese editions of the software formats it supports.