The answer is... Rance Quest was translated entirelly pretty much but final quests by the same guy who translated Sengoku and i played during the time, though the patch was removed from the page once he started working in Magnum(the add-on update that forces into re-playing game 3 times).
While he was working into this patch, Mangagamer reached the fan-translator, stopping all his projects, though they added him in their team. Also, another thing to consider is that his translations were sent to Mangagamer and also revised(his older ones) and he was placed to work in Rance Series in general there... so Magnum got placed "in line".
In the end, they released more than 4 different Rance games before this one being released... From Rance 5D to Sengoku i believe(all official this time) and they also released the re-makes of Rance 1/2 in english(i think it was a double package, or just Rance 1) before finishing this one... now, they only have Rance 9 and X(the end of the series) to work there in their project catalogue(rance related games). So can expect those 2 to be released faster than all these other ones that were pretty much released in same order japanese version got out pretty much, as official ones... The real answer to ur question of "why the fuck 10 years?" probably because Alicesoft enforced a contract on Mangagamer asking them to make official releases from the games in the same order the japanese ones were released and Magnum was later in line as the focus or whatever. They also priorized the introduction to Rance Series(1 & 2 Re-Make) than working into this one that is closer to how Rance X system will be thanks to the giant amount of characters and being the final game...
EDIT:
Almost forgot, they also have confirmed an Evenicle 2 official release, so, unscensored edition later by them. Probably will be released between Rance 9 and X or earlier than both, who knows?... since Evenicle 1 has been out for a while already anyway...(a spin-off from Rance Quest systems, same pattern but different story with newer hero and more vanilla content to who hates Rance personality)...