You could use:
- Alles Gute zum Frauentag/Weltfrauentag/...
- Alles Liebe zum Frauentag/...
- Ich wünsche Dir/Ihnen einen schönen Frauentag...
In my experience though, in Germany, this day is celebrated more as a day for women rights than as anything else.
Outside of feminists, communists, labour unions and the like, the day is perhaps best known among people from the former GDR and immigrants from East European countries such as Poland and Russia, where it was/is celebrated as a day for women.
In any case you might run into all kind of reactions with wishes for the "Frauentag": surprise, appreciation, disapprovement (rarely)... Few women would expect any wishes, but if you say it honestly or jokingly (like you might say "Happy Star Wars day"; May 4) you should not run into trouble.