Ok, I found the solution (by reading your tips
)
If I open a movie that has a subtitle file with the same name -> results the subtitle file is automatically opened by BSplayer -> subs editor menu items are ALWAYS in English.
If I open another movie (or don't let BSplayer to automatically load subs) and then I load external subtitles as you suggested -> subs editor menu items will be correctly translated :)
Thanks Peter for the suggestion :!:
Anyway this bug should be fixed