So I tested my plugin, written using English prompts and descriptions, with a Spanish query. My plugin does quite a bit of text processing, including calling google customized search api and calling openai gpt-3.5-turbo, sometimes with lengthy (English) prompts.
Much to my (happy) surprise, chatGPT seems happy to switch languages ‘on the fly’, accepting my English prompts and the Spanish user text, and presenting the final result in the original user query language. How cool is that! More testing needed, but seems promising. YMMV