There is no manual.

Additionally, I have yet to find a tutorial for creating english voicebanks specifically. English is a language that is incomprehensible when spoken using only foreign syllables.

How do I make an English voicebank without having to use Chinese or Japanese characters?

You don’t have to type vowels thrice, only twice.

As for English, you can use any phonemes/aliases you want, so long as your reclist adheres to the CVVX format that DeepVocal uses. Which is basically CVVC, more or less.