"¡Qué interesante es este idioma!"

Translation: This language is so interesting!

[ChristineA86]

Where is 'tan'

[RanjanaJai540447]

How is 'Qué' interchangeable with 'How', when it means'What'??

[Cerise743285]

What's the difference between "Lenguas" and "Idiomas" as I understand they both mean languages; and it what context should I be using each word?