Yes, the theme has language files.
However, I think I have solved the issue. I needed to wrap the strings that weren't getting translated ('Leave a reply', 'No responses' etc.)with a GetText call.
As so beautifully explained here:
How to Localise.
After I did that, however, some things were still showing up in the default language, English in my case.'Leave a reply' was not being translated. So, I decided to check the .po file and see what the transaltor had written. In the .po file 'Leave a comment' was written,whereas in my comments template I had 'Leave a reply' which is why it wasn't translating. I just changed'Leave a reply' to 'Leave a comment' in my comments.php template and voila, everything translated OK, so, if anyone else is having the same issue, check the.po file against your templates, you may have translation discrepencies.
That being said ,one of my initial doubts still stands.
Can WPlang be amended for more than one language?
Like this for example:
As I said, I have 3 languages for my multisite and everything is translating perfectly, but I only have one language defined in WPlang.
How could this be?