The notion of the forbidden fruit being an apple is not something exclusive of english christianity (here in Spain is also an usual misconception), as long as I've heard is something habitual in Western European culture as a whole.
The main explication that I found about this is related to something that the OP already talked about: the latin words malum/mālum which mean evil and apple and have a very similar pronunciation. The reason was the following:
Saint Jerome was one of the most relevants scholars of his time, being depicted in a huge number of paintings. He is also the autor of a translation of the Bible from the original Hebrew that started in 390 and was finished by 405. This translation into Latin is what is know as a vulgate, an edition of the Bible aimed to the people, not just for the scholars.
St. Jerome translated the original using the word malum (additional reference) which has given rise to the notion of the fruit being a apple.
This misconception was perpetuated in the ideas of European people mainly due to the work of the numerous painters who decided to paint this scene. For instance here you can take a look at the painting called The Fall of Men by Jan Brueghel and P.P. Rubens:
And also the very famous Adam and Eve by Albretch Dürer (link).