Spanish conversation always starts with the pilot calling in in Spanish. It is not the controller who selects a language.
That's all very well. Nothing to stop the controller responding in English though!
Take the Netherlands as an example, ATC is of a very high standard, particularly around AMS. If a pilot does make a call in Dutch the response from ATC is always in English. However, we shouldn't single the Spanish out here, the French are bad for it as well.
