After a short research/reading on the internet for myself, I found two ways to convert dictionary files to MOBI. Both involve two stages - one to intermediate temporary/raw files and the second from the raw files to MOBI.
Required software:
pyGlossary (for both options):
https://github.com/ilius/pyglossary/releases or
https://github.com/glowinthedark/pyglossary/releases
Kindle Previewer (for the first option) (terrible program):
https://www.amazon.com/Kindle-Previe...de=21381691011
KindleGen (for the second option):
https://cloud.freemdict.com/index.php/s/X93k2wPB9JR7kby or
https://cloud.mail.ru/public/r5sN/TZbEcVM4R
The first stage in both options is done with pyGlossary: open the dictionary file you want to convert with pyGlossary, and as target format specify Mobipocket (.mobi) E-Book. Specify a name for the desired target file that must be different from the name of the source file (otherwise you will get an error). In both options, the raw files will appear in a temporary folder with the name you specified for the target file.
Option 1:
Install Kindle Previewer. Run the program. In the settings (in the View -> Preferences drop-down menu), set the main device type to Kindle E-Reader with Portrait orientation. After you have opened the source file, set the desired name and location of the target file / temporary folder, and specified the Mobipocket (.mobi) E-Book format, press the Convert button. A folder with the name you specified in pyGlossary should appear in the location you specified. There are two subfolders in it - META-INF and OEBPS. There is a file named Content.opf in the OEBPS folder. Open the Kindle Previewer program you installed. Press the Open Book button. Find the Content.opf file and open it. Wait for the program to finish working, then in the drop-down menu, press File -> Export and export the file in Books (.mobi) format (the second option). You have received a file named content.mobi - rename it as you wish.
Option 2:
Unzip the downloaded KindleGen somewhere (you only need the executable file kindlegen.exe). Open pyGlossary, then open in the program the dictionary file you want to convert, and as target format specify Mobipocket (.mobi) E-Book. Specify a name for the desired target file that must be different from the name of the source file. Open the Options menu next to the Convert button. There, open Write Options. Open the folder where you unzipped the kindlegen.exe file and copy it. Paste it in the Kindlegen path (path to kindlegen executable) field. Click the OK button. Click the Convert button. After the programs finish working, the converted file will be in the OEBPS subfolder of the temporary folder you specified, under the name content.mobi. Move it wherever you want and rename it as you like.
If you want convert .mobi (=.prc - just rename .prc to .mobi) to StarDict (.IFO) format, so use this converter:
https://github.com/anezih/mobi2stardict/releases
I found a solution for creating dictionaries for PocketBook in .dic format from practically any dictionary too. From DSL or XDXF format using this converter:
https://cloud.freemdict.com/index.php/s/azSZaAzFtoMrfYY or
https://cloud.mail.ru/public/X8PZ/t8Zh4WJTt
And from StarDict to XDXF format using this one, then again using the above:
https://cloud.freemdict.com/index.php/s/mQN9QnX33qMJttH or
https://cloud.mail.ru/public/MPBu/GQt8EMQmz
You can convert to StarDict or other converter-compatible format using pyGlossary:
https://github.com/ilius/pyglossary/releases / fork:
https://github.com/glowinthedark/pyglossary/releases
Dictionaries you can find here:
https://cloud.freemdict.com/index.php/s/pgKcDcbSDTCzXCs or here (mirror):
https://cloud.mail.ru/public/M9fm/aDxp6vv1R
Additional links:
https://cloud.mail.ru/public/UVGg/o4gVwsUCy