The word "Adorkable" is a portmanteau of "Adorable" and "Dork." That neatly encapsulates this trope. Adorkable characters are "dorky" in some fashion. Maybe they're socially inept or shy. Maybe they're really clumsy. Maybe they have some really, really conspicuous character tic that tends to earn them weird looks. Maybe they're just so darn sweet, that it borders on embarrassing. Heck, maybe they're just an out-and-out Nerd. However, rather than making them an outcast, these quirks give the character an endearing vulnerability.
I do not know how to bring the translation as close as possible to the meaning of the word.