That is meant to be a folder diagram. There were originally folder emoji in there as well, but it appears that the forum software deletes emojis from your posts.
And yes, you can have english and japanese in the exact same folder, if you are using an English method other than Arpasing. Sorting them into different folders does make it more organized though, such as with Kasane Teto's voicebanks. If you install all of her voicebanks by the recommended method, they should combine into a single voicebank with separate folders for regular VCV, soft, powerful, and English. When you use Teto you are able to use any sample from any of those folders at the same time.