I started using it last year and I think others would benefit from knowing about it too.
Offline dictionaries(based on data from wikipedia, wiktionary etc.):
https://github.com/itkach/slob/wiki/Dictionaries
I use the Wordnet and SimpleWikipedia dictionaries along with the one for the Wiktionary in my native language.
Going on a tangent about the dictionaries(you can skip this if you're currently not interested on that):
They had a Malayalam dictionary, which was quite awesome for me, as I'm a Malayali. The dictionary is based on ml.wiktionary.org from 2021. Maybe there were not too many additions for the effort to make a new one.
The code for creating the dictionaries are also available in their github. I tried it out, but I'm on Opensuse Leap currently and installing couchdb seems tricky.
I also saw a python package, Pyglossary, which helps to convert dictionaries between opensource formats.
Wikipedia provides monthly dumps of zim files(used in Kiwix, another dictionary app. Not available in F-droid).
https://dumps.wikimedia.org/other/kiwix/zim/
I was able to use Pyglossary to convert those into slob files and use them.
So might be an easier way to get slob files, if slob files of Wiktionary or Wikipedia in your language are not available. Or if you want to update them. Data scraping is also avoided.
Something that I've wanted from a dictionary app for a while is the ability to add custom definitions for words that I may not have a dictionary for.
For example, I am told by a friend that the Finnish word "pimahtaa" means "to go ape shit". I don't plan on learning Finnish, so I don't need a whole Finnish dictionary.
Another less isolated example is how when I was learning Attic Greek, I wanted to build my own personal dictionary from the ground up, where the only words in it would be what I had learned and added myself, also allowing me to add new words.
It feels like a fairly simple problem to solve, but I'm not sure what to search for, I wonder if you have any advice, OP?
The dictionary app shared here has pre-compiled dictionary files. The files can be edited and new entries can be added through some tools, but the app does not have that feature.
Which dictionary apo do you use? Maybe it has some tools like that?
If you're looking for creating a whole new dictionary, then I think there maybe opensource tools for it on the net. Like writing your word and definition in a csv, xml or json file and converting it into some dictionary format.
Pyglossary supports converting csv/xml/txt files to some of the popular opensource dictionary formats.