There is no generic pronoun in Romanian and I believe no other Romanic languages have it either. 
The good part is that the messages can be somewhat rephrased to not include the gender:
E prima oara cand %{user} a postat. Bine a venit!
* It’s first time %{user} has posted. Welcome!
A trecut ceva timp de cand %{user} a fost activ - ultimul mesaj trimis a fost pe %{date}.
* It’s been a while since %{user} was active - last message was sent on %{date}.