Translation:On May the fifth, we celebrate our freedom.
Volgens mij hoort deze zin zo geschreven te worden: "Op vijf mei vieren wij onze bevrijding." (On the fifth of May we celebrate our liberation.) Het wordt Bevrijdingsdag genoemd.
"In Nederland herdenken we op 4 mei onze oorlogsslachtoffers; op 5 mei vieren we de vrijheid."
"Het is 5 mei: vandaag vieren we onze vrijheid."
This 'liberation' day was made to include a bit more than just celebrating the end of WWII relatively recently, IIRC around the same time it was downgraded from an annual national holiday into 'only once every 5 years everybody is off'-thing and the remembrance day became more generalized/inclusive instead of focused on WWII only.
Our 'independance' would probably be the independance of Spain, and is not really celebrated. Probably because it is rathet a long time ago..