The patch means that ideally you buy the game from the developer Saino (so they are more likely to make another one and its also only $15/€12 at the moment).
Once you extract the file from DLSite then you use the files from Jooop to overwrite some of the original game files, which contain the Japanese text, which will then change everything into English without the program knowing or caring about the difference.
A full release would be the full game with translation files already applied however that means its a pirated copy and Saino gets less sales.
They did seriously good work so I was happy to
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to them. What bits of the story I was able to understand from google translate and the like are right up my alley too so no pressure Jooop