Thanks for replying knc1! Here is what I did:
I first applied the jailbreak to Voyage (the very one you provided, with the link above), it completed without any problems and I updated the kindle back to firmware 5.8.7.0.1.
Then, under this thread, I downloaded acxe_7.zip, put the Update_acxe_7_install bin file in the Kindle directory. In the Kindle, the "update device" option remained greyed out though (and the bin file disappeared from the main Kindle directory when I connected the device to the computer again). By that time, it "finally" appeared to me

that this might not work with the Voyage. Still, I put the gtranslator.acx file (extracted from the zip file gtranslator.acx.kpw.zip) in the Kindle directory, under system/acw . That didn't work either.
Basically, nothing happened, Bing is still the default translation service, no change in the appearance of the menu options etc.
I hope I did something wrong. Is it supposed to work on Kv otherwise? That would be great indeed!