Hey Mods,
AFAIK, AGS uses the full text with the &number as the key in order to determine the translation. If the original file does not contain the number in the original (Italian) line then it won't find the correct English line. So what needs to be done is to update the translation file (from AGS, not the plugin). I make sure to copy the translation with the new number into the translation data structure so when you update the translation it should be in there with the correct values. After that it should work.
You will actually see after updating that the translation file that it contains two sets, the original ones and the numbered ones (probably the original in the beginning and the numbered in the second half). This is an AGS behavior, it would be the same if you were to go to the script manually and change the line numbers on your own. It's not something major, it just means your translation file is bigger and has irrelevant lines. I think the right place to add cleanup is in the translation component since it's the one generating the file. It's probably possible to think of a script that removes the unnecessary lines in your specific case.
Still, it should work after you update the translation file, so it's best to start by verifying that.