The idiom "as plain as day" means that something is very clear and easy to see or understand. Day and daylight are things that are common in daily life and daylight helps a person to see clearly.
"Idiomas" in English means "languages"
Languages
"¿Qué idiomas hablas?" translates to "What languages do you speak?" in English.
What/which languages
"¿Cuántos idiomas sabes? ¿Cuáles son?" means "What languages do you know? What are they?"
It means "I speak many languages."
Quiero salir contigo pero nuestros idiomas serian una barrera
It means "What languages do you learn in school?" in English.
Tu conoces muchos idiomas (informal) Usted conoce muchos idiomas (formal)
well, que idiomas hablan en ese pais means....what languages do they speak in that country?
"¿Cuáles son los idiomas de España?" translates to "What are the languages of Spain?" It refers to the different languages spoken in different regions of Spain, including Spanish (Castilian), Catalan, Galician, and Basque.
"What languages do you speak?"