It's not a phrase with a direct translation into English. However, you can understand its meaning by breaking down the words:
* Fort: This refers to a fortified structure.
* de: This means "of" or "from".
* France: This refers to the country of France.
So, "Fort-de-France" literally translates to "Fort of France" or "Fort from France". It essentially means that the city was founded by the French and historically had a fort.
However, the most accurate English equivalent would simply be "Fort-de-France". This name has become so ingrained in the English language that using a direct translation would feel awkward and less natural.