Hey there! I only just saw this now, but I'm one of the editors who worked on the English version. To clarify, Pirahus is originally written in Traditional Chinese and translated into English.
We added the quotation marks while working on the English translation because we also got confused when the main character is speaking, vs his internal monologue.
As you said it may be a lot of work but I'll forward what you said to the writer and see if they will consider adding quotation marks to the Chinese versions.