the benefits of reciting translated Koran
I don't think that the benefits of reciting translated Koran are the same as reciting it in Arabic.
Consider the Hebrew translation of the mourner's Kaddish. From,Anita Diamant: "Saying Kaddish":
"the sound and rhythm of this prayer are so deeply embedded in Jewish hearts and souls, some contemporary liberal Jews do read or recite the Kaddish as a private meditation and find comfort in it".
In my experience,the "sound and rhythm" of the Kaddish can only be truly experienced when this prayer is recited in Hebrew. Even if the individual reciting Kaddish doesn't know Hebrew, the mere reciting of this prayer in Hebrew ( usually out loud) can be a very emotional experience ( one that could never be evoked if Kaddish were recited in English).