There is an English side to 福娘 (hukumusume)'s traditional stories collection. There are a bunch of non-animal folk stories too -- there are stories that are all human, stories with a supernatural encounter, stories with anthropomorphized animals, and to really confuse things, stories with shape-shifting animals, some of which have a 'supernatural encounter' feel and some of which have a 'anthropomorphized animal' feel.
While the appearing characters go along with certain types of stories, I don't think they neatly break down along the lines of the Japanese terms (童話 douwa 'nursery tale' 民話 minwa 'folk tale' 昔話 mukashi-banashi 'old story', お伽話 otogi-banashi 'fairy tale'), and a lot of stories fit multiple classifications. Especially mukashi-banashi is essentially a catch-all term for
all traditional stories. In any case, 'douwa' and 'otogi-banashi' both mean stories for children, while 'minwa'/folk tales are not necessarily for children, but rather are stories handed down by oral tradition.
The index of English stories is really meant for Japanese persons who are learning or practicing English, but it's a complete list of the stories in translation. Generally speaking, the type of stories you're looking for will have an animal mentioned in the story title.
There
is an English edition of the site but it seems to have been abandoned over a decade ago and contains only one animal story (The Mouse's Marriage) so I don't think it's very useful, but it's
Hukumusueme fairy tale collection
I don't know if hukumusume can be cited for your research, but it does at least let you read (or sometimes listen to) the stories and find out their titles. It's a kind of janky website, but it is a great resource for anyone with an interest in Japanese folklore.
Edit: Oh. I thought there were no Spanish translations, and I still can't find an index for them, but there is at least one spanish translation:
タヌキの糸車 La carreta hiladora del tejón<福娘童話集 きょうの日本昔話>