It seems that due to WP changes, the way localisation files work has changed, which means that the translation instructions provided
here need to be updated. I understand that the second part of the po and mo file names is dropped, so now if you want localisation files for, say, French, you should name them fr.mo and fr.po, instead of fr_FR.mo and fr_FR.po.
I downloaded a couple of localisation files (which were named according to the old convention) and I spent a few hours trying to find out what I was doing wrong, before understanding that all I needed to do was rename them. So I registered here in order to post this piece of information, I hope it will save a few people from going through the same trouble.
BTW, it's also a chance to point out that I'm enthusiastic about this theme

It's probably the most customisable theme available, while its support and development circle is unparalleled; in addition, by taking advantage of html and css knowledge, one easily tweak Suffusion to whatever needed. So, many thanks for creating this theme
