Very curious and useful indeed, Brian!! It’s very difficult to find the proper translation… Obviously, one tends to employ the expression that is widely used in the target language, rather than the exact equivalent. "Thank you very much" in Spanish would be "se lo agradezco mucho"; but that’s too formal, too long to be taken in consideration.
Like anders, I’ve got a few comments. For Catalan we find "moltes gracies/moltíssimes gràcies", I reckon one could apply this superlative also to Castilian "Muchísimas gracias". As to Galician, "Graciñas" is a diminutive… I’d say it’s actually "Muitas gracias", but I’m not sure.
By the bye, on visiting the link on the left-hand side where it says "Spanish", I found some curious things. I thought that Spain in Arab would still be "Al-andalusí", in the same way as in Hebrew one says "sfaradit".
But, now that I see "gazteleraz" in Basque… Actually it’s the language "Castilian" what they’re translating. Then it’s "gaztelera"(language of the South Wind) and I’ve never heard a Catalan asking whether you speak "espanyol", but always "castellà".
And, finally, anders, how can a commoner like myself get to know as many languages as yourself?!? 
Regards,
WS.