I'm assuming you didn't actually mean "all Latin UTF-8 characters", because those are rather few, but instead "all Unicode characters", or at least as many as possible. (Just nitpicking: it's not "UTF-8 characters" but "Unicode characters" - UTF-8 is one of the encodings Unicode uses, it doesn't define any characters).
It's not so much a question of which application to use, but to have a font that has all Unicode characters (since editors generally only use a single font for the complete file), or rather, a sizable subset that covers most languages. MS Arial Unicode is one such font; it can be installed as part of MS Office (and maybe downloaded from MS, I'm not sure).
subject: Editor for diaplaying all the Latin UTF 8 characters