The law regarding translations, fair use, and copyright duration varies by country, so it is difficult to offer a clear answer to this question. I am answering this question assuming that US law is relevant and that the work in question is under copyright. (If the work is not under copyright then obviously you do not need to concern yourself further.)
US copyright law has a doctrine called fair use which allows use of copyrighted material without permission from the copyright holder. I believe that distributing a limited number of full translations of the dissertation at cost or at a loss (that is, not generating a profit) for academic research is not likely to be legally infringing. Let's look at the 4 factors involved in fair use:
- Purpose and character of the use: The use is non-commercial academic research, which is a point in favor of fair use.
- Nature of the copyrighted work: Seems irrelevant here.
- Amount and substantiality: You are suggesting translating the full dissertation. This does not necessarily disqualify the use as fair but you would have an easier time justifying distributing a translation of part of the work. Incidentally, this would also reduce the cost of translation so you may want to go this route.
- Effect upon work's value: I believe this limited translation would increase the original work's value because it would increase its market size, so I think this is a point in favor of the translation. Note that this may change if you were to post the translation online for anyone to download.
The most legally justifiable way to publish a full translation would be to make one printed copy and get it put in a library. This used to be relatively common (I've received translations via interlibrary loan that were published this way) and I'm not aware of any legal challenges to this approach. This approach minimizes the effect on the market for the original.
Note that I am not a lawyer and this is not legal advice. You should ask a competent IP attorney in your local jurisdiction if you want a better answer. If you are at a university, your university may have one or more staff attorneys who could answer this question for you at no cost to you.
Note that it still is polite to get permission from the copyright holder and/or author(s). I have published quite a few translations and while it is rare that I am able to contact the authors (usually the papers I translate are quite old and the authors have been dead for a long time), I am yet to encounter any author not enthusiastic about translating their work. I don't recall ever getting a response from publishing companies about translating work they own the copyright to.