I’ve come into a decent stack of technical dictionaries. English to Italian, German, Spanish, Russian and Turkish.
Most of them are about 50 years old. Is there any market for these? Am I sitting on a goldmine? Or am I just sitting on a pile of paper?
The think the used book stores sell stuff like that for decoration at about a $1 a linear foot. Somebody would have to look at all the books to tell you a value. Most older books aren’t worth much.
That is a somewhat debateable statement. In any case, I’m looking around on Amazon, etc for values. A couple of them are $300+
Anyone need a Taspinar’s Technical Dictionary Turkish-English? 
A rule of thumb I’ve heard is that regular dictionaries should be replaced after 25 years, to catch up with changes in language usage. I would expect technical language to mutate at least as regularly as everyday speech, so I wouldn’t rely on 50-year-old dictionaries for reference use.
They could be worth something as collectors’ items; any old book is potentially worth something as a collectors’ item, and any collectors’ item is “worth” whatever you can persuade someone to pay for it. Some sellers are more persuasive than others, which is why the price of used books can cover a wide range.
You had me until the end. Oh my kingdom for Taspinar’s Technical Dictionary English-Turkish
Mock me if you will, but today I sold an Elsevier’s Maritime Technology Dictionary (English, French, Italian, Spanish German) on Amazon for $200. 