In Spain, there isn't the circus surrounding the appointment of Supreme Court judges as there is in the US but there is a similar concern about the political nature of appointments, and this politicisation is an issue identified by the European Commission in its latest report into the Rule of Law in EU member states.
The report has reserved eleven pages for Spain and it highlights, for example, the importance of ensuring that Spain's General Council of the Judiciary is not perceived as being vulnerable to politicisation. There is consideration of the relationship between the Attorney General and the Spanish government, as the appointment of an Attorney General and the ending of his or her tenure are linked to a government's period in office. This, as the report notes, "can affect the perception of independence".
These reports were prompted by various factors, one of which was Catalan secession. The latest report, while it considers matters such as the prosecution of corruption and organised crime, avoids making specific reference to the Catalan question. Coincidental though the timing of the report is, given the anniversary of the referendum, it is nevertheless pertinent in alluding to the importance of impartiality and freedom from interference not only existing but also appearing to exist. Which isn't to say there was interference with the cases of the Catalan secessionists, but that it was essential that there was no appearance of any.
The separation of powers is a fundamental principle and has to be seen to function in practice.