I am maintaining the script PocketBookDic to convert dictionaries to xdxf-, Pocketbook dic- and Stardict ifo-format. It's at the github repository
PocketBookDic.
Conversion to dic-format needs a windows program
converter.exe and language configuration files. They can be found at the github repository
LanguageFilesPocketbookConverter.
Nowadays, I am looking into more heuristic approaches to convert free format dictionaries, such as mobi-files and Kindle dictionaries (azw-, azw3-files). Typically it has an intermediate html-stage, which has to be interpreted and converted to the central xdxf-format, before it can be converted to other formats such as Stardict optimized for Koreader, Pocketbook dic-format or mdict-format.*
Over 20 dictionaries in both xdxf- (human readable), Stardict- and Pocketbook's dic- (binary) format can be found here. (The xdxf-files can be converted with convert.exe to the dic-files. If you want to tweak your dictionary, this is the place to do it.)
16th November 2021: Getkey just did some testing and the scripting for pocketbook format is updated to handle unicode characters better. All pocketbook dictionaries are recreated.
For those that can't be charmed by the tinkerings needed for conversion, post a request and link to your dictionary files and I'll try and convert them.
11th November 2022:

Due to an excessive amount of traffic (more than 50GB this month) pCloud is restricting access. As it is a moving total, access should be restored within a few days. (The last 2 days in the graph show restricted access. Apparently, nobody is going to pay for pCloud.

)
November 13th, 2022:
pCloud access is indeed restored.

.
January 8th, 2024:
Link to mirror of the pCloud account on 8th of January '24
Hopefully this will spread the traffic.
March 7th, 2024:
This one of the links to the 6.5GB stardict-tarball floating around the internet for over a decade. This is the starting place for checking whether a dictionary is available in Stardict format.
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*Only implemented to check whether there would be a speed improvement over Stardict on Onyx Boox systems. It didn't improve.