Asking about good offline dictionaries in Ubuntu would have created a duplicate of this question which got as answers only Goldendict and Artha.
Artha is ok but is limited to English as far as I can tell.
I would like at least some more English and French dictionaries.
I have also installed Opendict but it asks to add dictionaries. How to do it?
Many users recommend Goldendict, which comes with Wikipedia and to which I could add an English dictionary,
but for dictionary sources we are redirected to an almost dead website: most of links are dead and/or in Russian. I cannot download any dictionaries from Babylon as they just give a link to download Babylon.exe no matter what "free-dictionary" I choose. I have extracted the exe file but no .bgl files inside (what am I missing here?).