This may be something of a pointless topic, but I'm interested to see if anyone knows anything about it.
Is the word 'yosh' an actual word? And does it occur outside the One Piece anime? I've only read a little of the manga, but it doesn't seem to be translated. I can think of a number of things it could be:
a) An exclamation invented by Oda for some reason
b)A Japanese word that has no easily translatable meaning, so like 'nakama' is left untranslated by fansubbers
c) "Engrish" for 'yes'- given the large amount of engrish used in OP in general, this seems quite likely.
Or maybe it's just another One Piece mystery, like Sanji's eyebrow.