I noticed even in the Englished Dubbed version of One Piece many of the props (flags, signs, etc) use Japanese symbols rather than alphabetical words, and now, watching on the Subbed version, I notice some things are actually written in English. For example an island entrance says "Punk Hazard" and "Danger" in English, even though they're speaking Japanese.
I've noticed this kind of inconsistency elsewhere too, for example, even in the Subbed version, you hear many English words and names, such as their shipwright saying "Super!". I've nopticed more things like this throughout the entire series, having watched many episodes in Dubbed and Subbed versions.
So, is there an explanation for why English and Japanese are intermingled so heavily in One Piece? it seems odd for the text to be inconsistent. Maybe they produced a few different versions with different text forms, but that would be odd since it's not even an English dubbed version in some cases.
Was the writer bilingual? Or was it perhaps a strategy to please English and Japanese viewers equally? Or some other reason?