der April
April
The fourth month of the calendar year.
Mein Geburtstag ist im April.
My birthday is in April.

April
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April
The fourth month of the calendar year.
Mein Geburtstag ist im April.
My birthday is in April.

When talking about events that take place in this month, you use the preposition 'im' (in dem). This applies to all month names.
Im April fängt der Frühling richtig an.
In April, spring really begins.
The idiom 'jemanden in den April schicken' means to play a joke on someone on April 1. The person being tricked is in the accusative.
Ich habe meine Kollegen mit einer falschen E-Mail in den April geschickt.
I played an April Fools' joke on my colleagues with a fake email.
In Germany, April is known for its changeable weather. A well-known saying about this is: 'April, April, der macht, was er will.' (April, April, it does what it wants.)
Erst schien die Sonne, jetzt hagelt es – typisch April!
First the sun was shining, now it's hailing—typical April!
prank / stroke
'der April' and 'der Streich' are similar only in one specific context: on April 1. In the expression 'jemanden in den April schicken' (to play an April Fools' joke on someone), 'April' means that you play a prank on someone or tell them a false story. 'der Streich' is the general word for this kind of funny or annoying action. 'April' on its own is normally just the month. If you are talking about the action, 'Streich' is more precise; if you mean the fixed expression, you use 'in den April schicken'.

Am ersten April hat mich mein Bruder mit einer falschen Nachricht in den April geschickt.
On April first, my brother played an April Fools' joke on me with a fake message.
Der Streich war harmlos, aber alle mussten darüber lachen.
The prank was harmless, but everyone had to laugh about it.