How are footballers who are Spanish nationals taxed ??
On paper it should be uniform (in which case said players may merely
being paid much more in wages) .
It all seems to be about some sort of image rights dodge, where they're getting paid into overseas accounts.
I'm not sure if the nationality of the individual makes any difference, to be honest.
Correct. The watershed moment was when the Beckham Law was effectively scrapped in 2010 when the recession began to really suffocate the Spanish economy. From 2003 until that point, professional footballers could opt to pay non-domicile tax rates of just under 25% on all image-rights income. In 2010 this was scrapped for players earning more than 600,000Euro p.a. on those rights (most top players earn far, far more than this via various sponsorship deals and endorsements), which is why most of the allegations trace back to the 2011 tax year onwards. (As a side note, the Beckham Law was scrapped entirely for all professional footballers as of Jan 2015, as the courts began wising up to the fact that the overwhelming majority of players who play for Real & Barca are cheating bastards both on and off the pitch).
The controversy has arisen because all of the aforementioned players/manager have registered various offshore smoke n mirror 'companies' through which they funnel income related to image rights. Since the 'fall' of the Beckham Law, these monies should be subjected to the usual tax rate of 51% for top earners (ironically this is actually 56% in Catalonia). The accusation is that Messi, Ronaldo, Maureen etc. failed to fully declare image-related earnings, quite literally making up percentages of how much of said income was 'earned on Spanish soil' and how much was not.
The prosecution is arguing (quite sensibly) that since the overwhelming majority of said image's physical exposure was accomplished playing in Spain and for a Spanish employer, image-rights should legally be considered equivalent to money earned on Spanish soil and thus taxable at the full rate as per normal salaries - irrespective of how many mickey mouse accounts the money visits before being spent on champagne, cars and egocentric statues.
The defense is arguing (somewhat less sensibly, although I do see their point) that the totally globalised nature of the game and exposure of said image makes it impossible to trace the fiscal gain of said image to any particular sovereign state, and the bulk of these monies are therefore regarded as if earned 'overseas' and not taxable under Spanish law. There is some sense behind this argument as - for example - Messi is paid millions a year to wear Adidas boots because the executives at Adidas anticipate that he will be wearing them while playing Germany or France in the World Cup and will be seen by an audience of hundreds of millions. Messi wearing Adidas boots against Granada understandably attracts far less interest and QED that 'image' is worth far less in Adidas' eyes.
The reason why the defense's argument is doomed to fail is that they are simply regurgitating the logic of the Beckham Law (at the time of his move to Real, his lawyers correctly pointed out that he was an already-established mega-brand and should therefore be exempt from the highest rate of tax). The Spanish government very generously opened that particular loophole during the years of plenty. But it has now been irrevocably closed. Don't like it? Piss off and go play elsewhere.