The Spanish Constitution gave hope to enlightened Russians for building a just society in their Fatherland. So, if the Decembrists "awakened" Herzen, then the Decembrists themselves were "awakened" by the very boldness of Spanish democracy. In the opinion of some historians, the project of the Russian constitution by Prince Sergei Trubetskoy was partially based on the Spanish law of 1812. One of its main points is almost word-for-word taken from the Spanish version of the document: "The Russian people, free and independent, are not and cannot be the property of any person or family" - "Nación española es libre é independiente sin ser ni poder ser patrimonio de ninguna familia ó persona (The Spanish people are free and independent and do not belong to nor can belong to any family or person). The Spanish Revolution of 1820 added fuel to the fire, as during which military and liberal-minded segments of Spanish society managed to get Ferdinand VII to restore the "Constitution of the Cortes" of 1812. One of the Decembrist leaders, Pavel Pestel, literally dreamed of a Russian version of "pronunciamiento" (coup). He admitted that he believed in the realization of his plans, relying precisely on the example of the Spanish Revolution. The Decembrists often compared themselves to the leader of the Spanish revolutionaries, Rafael Riego. Many even believed that Sergei Muraviev-Apostol "resembled the Spanish hero closely and accurately." So, the Spanish Revolution can be considered one of the factors that influenced the events of December 14, 1825. In fact, it was the Spanish Revolution, not the French one, as the Decembrists believed that Napoleon's conquests were doomed.
https://little-histories.org/2016/05/13/tristeza_espanola/