There are many little parts of a language that you come to know when you live in the country itself. But they are indeed an essential part of a language. They carry strong emotional content that is direct and immediately meaningful. These are often very short phrases or sometimes just one word.
Here are a few examples commonly found in French:
Aïe ! Ouille ! (Ouch!)
(Et ben/bien) Ça alors ! (Wow!; Well really!)
Mais/Bah oui ! (Why yes!)
Comme c’est bon !/Que c’est bon ! (How tasty!)
(Mais) Enfin ! (When outraged, annoyed as in: “For God’s sake!; What do you think you’re doing?!; Cut it out!)
Zut (alors) ! (Damn!)
Hein ? (Huh?)
Ouf ! (Phew!)
Ça y est ! (That’s it!)
Tant pis. (Too bad; oh well)
Miam-miam ! (Yummy!)
Adieu (Farewell, but more like it may be the last time)
Coucou ! (Hello!, Peekaboo!)
Si ! (Yes, as in affirmation of the contrary)