Basically probably the same problem that Jellyfin is facing now https://github.com/jellyfin/jellyfin/issues/4822
Moviebase wont use fallback if there is NO translation availible and will show placeholder string instead. As you can see on screenshot here, there is placeholder text “Epizóda 1” and not episode name from fallback language (for example english).
More screenshots on Jellyfin git and on imgur link (limit 1 pic for post for me so… this was the solution https://imgur.com/a/cDSq6rm )
Also, when is translated only episode title and not overview it seems to be working correctly, fallback language was used = english.
Curiously, this seems to be working correctly in movies in moviebase, as you can see here. Movie had only translated Name on TMDB, not overview. So fallback language was used = english.
Tested on latest BETA version 2.6.5.