You are correct.
I re-read this report:
Ryanair B738 at Alicante and Valencia on May 14th 2010, fuel emergency | AeroInside
The CIAIAC thus annotated: "The fact that English was not used in the communications kept RYR 9ZC from understanding the more explicit and colloquial information that was being given to the other aircraft. That is why it would be convenient that, when aircraft converge at the same airport and whose crews speak different languages, English be used so that all have the same information and all benefit from the information provided to other crews."
The Spanish Authorities merely suggested English 'would be convenient' but didn't point to a regulation.
I stand corrected on the ICAO point.