Which is a fine explanation until it comes to explaining how they manage to do things like know our alphabet goes A B C D E..., for example.
Well, they don't necessarily need to go through the intermediary step of converting morse -> 'latin' letters. Assuming a reasonable level of intelligence and availability of enough encoded data (of which they have plenty!) they could deduce the existence of 26 unique characters in our letter-set. They'd only need to ever intercept a handful of broadcasts of 26 characters, with each character featuring exactly once, in the same order to deduce that is our letter-set in its alphabetical order, and use that to plot the ship schematics.
But still, they're never dealing with As, or Cs, just ".-", "-..." and "-.-." etc.