Okay, I had a look at the days and months and transifex.
Again, no good way to fix it except rewrite the arrays and do some "hack" in the code.
I tried also the form:
$txt['days'][0] = 'Monday';
but transifex doesn't like that as well.
So, the only thing I can think of is:
$txt['monday'] = 'Monday';
And then in load, just after the index file is loaded, fill the normal "days" array:
$txt['days'] = array($txt['sunday'], $txt['monday'], etc.);
Opinions?