Download pyGlossary:
https://github.com/ilius/pyglossary/releases
or the fork of pyGlossary:
https://github.com/glowinthedark/pyglossary/releases
- as an installation file or as a portable application (.zip), it doesn't matter.
Start pyGlossary and open the .dsl or archived .dsl.dz file as input file. The program will automatically recognize the extension. In the bottom field, specify the folder where you want the file to be converted, and as the extension using Select Format, specify StarDict (.ifo). Click Convert. That's all.