Not at all. In 1789 various nations recognized letters of marque and reprisal.
They were used in an attempt to stop Muslim terrorist pirates from attacking our shipping in the Mediterranean and the African Coast (the Barbary Wars).
However, they were not very effective and the Marines had to be called in to stop the piracy (hence: "From the halls of Montezuma/ to the shores of Tripoli").
It wasn't until the Declaration of Paris in 1856 that all the European powers stopped recognizing letters of marque and reprisal.
From that point on, no nation has honored another nation's letters of marque and reprisal, and such letters are now utterly useless.
Again, letters of marqure are not for the purpose of gaining the legal respect of other countries, but to authorize one’s own citizens privately to undertake the forceful reclamation of property.