You can say "Soy maestro jubilado", or "Soy maestra jubilada" for a female.
Feliz Jubilación
Happy Journey
Depending on the relationship with the person retiring, would determine what to say in a written Happy Retirement. If the relationship is not a close on, a simple "Congratulations and Happy Retirement" would be sufficient.
Happy retirement! translates as Alles Gute für den Ruhestand.
If you want to say happy retirement in Italian you would say, pensione felice. You would say good luck by saying buona fortuna.
gelukkige aftrede
Feliz aposentadoria.
Deseo que tengas un jubilación feliz.
Feliz jubilación! or simply "Felicidades!"
In finnish: hyvää eläkettä
feliz
I'm happy too in Spanish is Estoy contento también.
Estamos contentos.