Let's take some of these points in turn.
My co-author is claiming to be the sole author.
That's not right -- neither of you is the author. By conflating the difference between author and translator, aren't you doing a disservice to the author roughly similar to what your professor is doing to you?
I should also say that in my academic field (mathematics), translating a text is viewed as service to the community rather than an intellectual or academic contribution per se. I know it is different in the humanities.
The professor claimed to have "reworked" my translation and we are both credited on the title page as translators.
Why "claimed" -- did he or didn't he? You seem to be a bit breezy on your description of the work that the professor did on this project. Again, it would be better to be clear. If the professor didn't actually change your translation, then the translation should be attributed only to you, right?
The professor wrote an introduction and edited the translation so the professor's name is also on the title page as editor.
So the professor edited the translation. I wonder if there is some subtle distinction between "editing" and "reworking" that I am not appreciating: does the latter imply a larger intellectual contribution? Again, how much of an intellectual contribution are you claiming the professor made? That seems important.
From my standpoint in a STEM field, it seems like editing a translation is a contribution of about the same order of magnitude as writing the translation...but again, I tend to think of translations as being somewhat routine work for those who have language skills. Maybe I am missing some nuances here. But certainly writing an introduction and finding a publisher is a big part of, um, getting a work published. So from what I understand it seems reasonable that you are both listed as translators on the title page.
Recently, it has come to my attention that the professor, who is now an emeritus professor, is claiming to be the sole author.
That's a very strange claim to make when the book itself says otherwise. In my experience, academics are highly attentive to bibliographic information like this.
I recently attended a conference where the professor gave the keynote address. I recently attended a conference where the professor gave the keynote address. The professor was introduced as the sole author of this book.
I'm not sure I understand what you mean. First of all: really as the author of a translated work? Second of all: do you mean "Professor X's book Y, which is [hopefully something about a translation of someone else's work!]" or "Professor X is the sole author of book Y, which is..." The latter would be a really weird thing to say even if it were true, and the former, while not very nice to you, need not be construed as denying your role.
However, I recently came across the professor's written biography on the internet where the claim is made that "[the professor's] book presents an edition, translation and . . . commentary" of the treatise.
Again, this does not strictly imply that you were not also an author. Whether this is okay may depend upon how formal the document is. If it is formal enough to give bibliographic citations, then your name should certainly be included in the bibliography.
Should the professor mention my name in connection with the translation in such a circumstance? If so, how do I go about getting the professor to do this?
Is this biography written by the professor or by someone else? If it's by someone else, you should just send them the bibliographic reference, perhaps accompanied by an electronic copy of the title page of the book.
should mention that the professor has done many collaborative projects and in every case other than our book, the other collaborators are mentioned in the biography. Also, there is a long history of my having to remind this professor to acknowledge my work. Before our book was published, the professor gave a conference paper on the treatise and didn't mention that I had translated it. When I call it to the professor's attention, the professor said it was an oversight. The next time it happened and I mentioned it to the professor, I was told that the project could have been done without me. Every time it has come up, there is a new excuse.
That sounds horrible, and there is no doubt that the professor is behaving inappropriately. "[T]he project could be have been done without [you]" is by no means a justification for not including a coauthor's name! No reputable academic would accept that answer.
My question is whether it is worth pursuing since my name is on the title page of the book itself as a co-translator and other scholars will see it there. It really bothers me that the professor is claiming credit for my work by omitting my name.
You raise a key point: you've described various venues in which your coauthorship was not mentioned, I believe inappropriately, but these are all rather informal. As I mentioned above, academics are very formal when it comes to bibliographic issues. When the work is cited in other academic works, both you and your professor's names appear, right? (If the work is not cited in other academic works, after this many years it might be best to let it go.) So I don't think there's a serious risk of loss of your academic reputation. (Note that you don't say whether you are currently an academic, so the consequences of a loss of academic reputation to you are a little unclear.)
Honestly, I think you should do something else if and only if you are very upset with the professor. If so, I would begin by writing to him along the lines of the current message: remind him of the facts of the situation, tell him that his behavior has been distressing to you for many years, and tell him that you want your name mentioned along with his. Be prepared for that not to go very well, of course. If it doesn't, well then you can fight webpages with webpages: you can make a webpage where you describe the situation in enough detail to firmly convince a reader that you are in the right. I have occasionally seen such webpages by academics, and if they are done well they certainly have an effect on the community's views. They also reveal to the entire world how upset the writer is with the situation, so definitely think several times before engaging in this.