In
自信があれば半ば成功したも同然だ。
Confidence is half the battle. (Idiomatic translation)
I'm having trouble getting to the idiomatic translation.
It seems like a good literal translation of the clause before も is:
自信があれば半ば成功した
If one has self-confidence, one does success halfly.
What role is も playing? Translating it as "too" or "also" seems a bit awkward to me (i.e. "if one has self-confidence, one does success halfly too" is a bit weird?).
What is the 同然だ doing at the end? Does it mean something like: "it is natural", so that the overall sentence becomes: "it is natural that if one has self-confidence, one does success halfly"?