We are speaking uncontrolled, so towerless, airfields in Spain, aren't we? Then it all depends on the AIP settings for the specific airfield. Although most european countries decided to set prime language to english, this is typically limited to a defined set of frequencies. There was a long discussion last year with the french fighting brits without LP french in their license, but flying to FR only fields.
The way I remember flying to small airfield in Europe I had to look up each and every to find out what languages are provided at the field. If I also remember correctly, with Language Proficiency regulations in EASA land, you have to have the LP entry for the language used at the airfield to be allowed to execute your license rights for landing, unless there is a COM NOOP allowed.
I remember also seeing many airfields with opening hours for different languages - most prominent if there are too few people speaking a specific language. Even further, there is some setting which allows any official language to be set mandatory for a field. A friend once told me they thought of declaring a small airfield in northwest Germany as Saterfriesisch only, which is a very small local minority language and they checked this to be legal.