Is "My hobby horse" an idiom? What does it mean in Spanish?
My hobby horse....
I have no idea what it would be translated to. I guess it would have to be translated to the word for the old-fashioned children's toy by the same name.
Here is the definition I found in case anyone fluent wants to translate:
on your hobbyhorse if someone is on their hobbyhorse, they are talking about a subject which they think is interesting and important, and which they talk about at any time that they can, even if other people are not interested (Don't mention tax, or Bernard'll get on his hobbyhorse again.)
It is one of those funny expressions that we know immediately what it means in English. However, when we stop to actually dissect the words, it sounds strange.
Also, according to this definition for idiom, I would say that "hobby horse" falls into that category: Idiom definitions
Our dictionary has this to say about "hobby horse":
caballo de batalla -> bone of contention; (dificultad, escollo) hobbyhorse (objetivo, obsesión)
You can see the full definition of "horse"/"Caballo" here ----> Caballo