The language of Argentina is Spanish. However, each Spanish speaking nation typically has their own dialects and form of the Spanish language, which would make some words of phrases different. An example is the 'Happy Birthday' song.
In Argentina the lyrics are as follows:
Qué los cumplas feliz
Qué los cumplas feliz
Qué los cumplas (name)
Qué los cumplas feliz
Don't forget the lyrics in English:
Happy birthday to you
Happy birthday to you
Happy birthday, dear (name)
Happy birthday to you