Final answer:
The text does not explicitly mention a specific venue where Caitlin learned the language of her hosts. However, immersive experiences during her social interactions in Spain likely played a key role in her language acquisition.
Step-by-step explanation:
The venue where Caitlin best learned the language of her hosts was not specified in the text provided. However, it can be assumed that immersive experiences like the dinner at Maria's family's house, and other social interactions in Spain, were significant in helping her learn the Spanish language and understand cultural nuances. Similarly, Mrs. Ebbling's mention of living in Naples and experiencing the city alone suggests the idea that immersion in the local environment is a powerful way to learn a new language and culture, as was the case for the protagonists experiencing different languages and cultures in Vevey, Switzerland, and amongst 'Cadian ball attendees, among others.