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.
"Maligayang pagreretiro" is how you say happy retirement in Tagalog.
In Flemish, you can say "Gelukkige pensioen" to wish someone a happy retirement.
In Afrikaans, you can say "gelukkige aftrede" to wish someone a happy retirement.
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.
Feliz jubilación! or simply "Felicidades!"
You can say "joyeuse retraite" in French to wish someone a happy retirement.
In finnish: hyvää eläkettä
"Feliz aposentadoria."
Irving Salomon has written: 'Retire and be happy' -- subject(s): Retirement
You can say "Soy maestro jubilado", or "Soy maestra jubilada" for a female.
"Happy retirement" in Portuguese is "feliz aposentadoria."