As a historian of biology—of mostly the 19th and 20th centuries, and of mostly German biology, a little bit of English- and French-language biology, and teensy-weensy bits of Dutch, Czech, and Russian biology—I rely a lot on multilingual dictionaries to help me understand my sources. I think old, digitized dictionaries are invaluable for doing good history of science, because they help us understand terms as they were.
If you have a number of them across different editions or eras you can even track how these terms change.
Most pre-1930 dictionaries are now available digitized online, but I also make an effort to do my own scans when I can’t find them. I keep a separate folder in my Zotero database so I can do an indexed, full-text search of all of them with one search action.
The two I reach for most often have been:
- Artschwager and Smiley’s Dictionary of Botanical Equivalents, 1921: English, French, German
- Artschwager’s Dictionary of Biological Equivalents, 1930: German-English
The Artschwager dictionaries are concise in a good way. When I was a grad student I relied on the Dictionary of Biological Equivalents almost exclusively, until I realized that Zotero allowed me to search a bunch of dictionaries at once. Artschwager is concise that it’s not very helpful for 19th century stuff. For that I go to:
- Treves and Lang’s A German-English Dictionary of Medical Terms, 1890
- …which can be compared the 3rd edition Lang’s German-English Dictionary of Terms Used in Medicine and the Allied Sciences, 1924
I’ve also added two specialist dictionaries:
- Patterson’s German-English Dictionary for Chemists, 1924, because I don’t do a lot of history of chemistry before 1900
- Elsevier’s Dictionary of Microscopes and Microtechnique, 1993: English, French, and German. This is my latest addition, and it’s really great.
- Conn’s Biological Stains, of which I found the 1936 edition already digitized, but the 1961 edition is sort of available for blind searching.
And finally I’ve lately kept Brandt’s German-English Dictionary (1925) as a last resort, for when dict.cc, BeoLingus, and Leo all manage to fail me at once.
What would you add to my list? What do you use?
Daniel Liu, History of Science 
As a check on German-English translations, I have found it useful to look at German-German technical dictionaries. The one I have used most is H.E. Ziegler’s Zoologisches Woerterbuch. Erklaerung der zoologischen Fachausdruecke (Jena, Gustav Fischer, 1909). My German dissertation mentor Hans Querner, an embryologist turned historian, insisted it was not a good dictionary because it was “inaccurate,” but it was never clear to me whether he thought is was inaccurate at the time or inaccurate for later purposes. I have found it helpful.
Added!