The are nicknamed and name themselves "Die Eisernen" i.e. "The Iron(men)", hence you will see Eisern / Eisernen quite often. Eisern Union means "Iron Union" (similar to Iron Maiden)
Machine translation ...
We from the East always go forward
Shoulder to shoulder for Eisern Union
The times are hard and the team is hard
That's why we win with Eisern Union
Eisern Union
Eisern Union again and again
Always further forward,
Always further with Eisern Union
Who always plays at full throttle?
Eisern Union, Eisern Union
Who likes to score an extra goal?
Eisern Union, Eisern Union
Who lets the ball and the opponent run?
Eisern Union, Eisern Union
Who won't let the West buy them?
Eisern Union, Eisern Union
Victory in sight, looking far ahead
Let's move through the nation together
East and West - Our Berlin
Together for Eisern Union
Where does it smell like burnt grass?
Eisern Union, Eisern Union
Where we sound the attack
Eisern Union, Eisern Union
There can only be one
Eisern Union, Eisern Union
We will live forever
Eisern Union, Eisern Union
Eisern Union Always
Eisern Union Always further to the front
Always further with Eisern Union