When used as a noun, a rubberstamp is a device for stamping ink on paper, something children and bureaucrats love. A rubberstamp does not have to made of rubber, a simple potato will do, but rubber lasts longer. I admit that I usually do not like rubberstamps, although I once got a rubberstamp on my cartilla militar that stated that I was INUTIL, that is, absolutely useless, that still makes me happy (in German that would probably have to be translated either as untauglich or as im Kriegsfalle nicht ein Mal als Geisel zu gebrauchen). A rubberstamp in that sense is a Stempel or a Stampiglie in German and a sello or a timbre in Spanish. Although both sello and timbre have other meanings as well there is not much room for confusion, the context usually resolves the unambiguity.
The problem when translating rubberstamp arises when the word is used as an adjective (or a verb), like in rubberstamp parliament. This is a derisory term to indicate that the parliament in question does not fulfill its duties as a control organ of the executive branch of government. That is the case when the rubberstamp parliament approves everything the government wants it to approve without any control of the legitimacy of the bills proposed. This is unfortunately rather frequently the case in undemocratic regimes, where so called "toy parliaments" defer to the political masters of the state. That kind of parliament could be translated into Spanish as parlamento de pacotilla. Conversely, in a constitutional monarchy like Spain or Belgium, the monarch is typically a "rubber stamp" to an elected parliament, even if he (or some day she) legally possesses considerable reserve powers or disagrees with the parliament's decisions. In a parliamentary republic such as Germany or India, the President is also sometimes described as a rubber stamp. In those cases the term de pacotilla would be grossly unfair to the constitutional order, it is the President's or King's mission to rubberstamp the laws adopted by parliament. The only thing the rubberstamp king or president can do is to defer the signature as long as possible or to resign. The former German president Horst Köhler refused the signature of a bill on 24. October 2006 because he considered it (it concerned the privatisation of the German flight control) unconstitutional. The Belgian king Baduin did the same when he had to sign the bill legalising abortion, but not because it was unconstitutional, but because he was such a good catholic. He even went so far as to resign, only to be reinstated as a monarch after the bill was adopted during his leave. If that sounds hypocritical to you, we agree.
But disgressions apart the question remains: how do we call a rubberstamp parliament, a rubberstamp president and a rubberstamp king in Spanish or German?
It is fortunate that the Europan Parliament is not a rubberstamp chamber, otherwise they would need 23 different stamps, one for each language. I guess these would become coveted collectibles.