Here is what he is singing:

Let the pedestrians walk clumsily through the puddles
And let the water run over the asphalt in a river.
It's unclear to the passersby,
On this rainy day,
Why I'm so happy.

But I'm playing the concertina
For all the passersby to see.
Unfortunately,
Birthdays
Only come once a year.

I wish that a wizard
Would fly in, in a light blue helicopter,
And show a movie for free.
He would wish me a happy birthday
And probably, leave as a present
500 ice cream sandwiches.

But I'm playing the concertina
For all the passersby to see.
Unfortunately,
Birthdays
Only come once a year.