Unfortunately for Catalan, whilst it is recognised as a language, it is not accepted as an official language by the EU, much the same way as Welsh. See link: http://europa.eu. It is tolerated/allowed? by Spain because local peple have a greater command of the use of the language being used, much the same as Welsh. Hence, the dual format forms that you can receive in England, and because of the further devolution of Catalunya from Spain, than Wales from England, this allows the local beaurocrats to offer forms only in Catalan.
By the way, if anything legal comes along, you do have the right to insist that the form you sign is written in English by an approved organisation. Whether or not the trained monkey who gives you the form will comply with this or whether you get any joy out of their boss, is another thing completely.
The last paragraph is true, because, paradoxically, the self same Welsh and Catalans have used this plank of argument to get forms into their own language in the first place. They reckoned they were being penalised for signing forms they didn't totally understand ie being in English and Spanish respectively.