So he’s called different things in different languages. Cristoforo Colombo in Italian, Cristobal Colón in Spanish, Christopher Columbus in English. I can handle that.
But I don’t get this part: they speak Spanish in Colombia. Why didn’t use the Spanish version of his name as the base when they named the country?
If you expected “Colonia” instead of Colombia I´ll inform you that in Spanish that would be syntactically incorrect since a “n” can´t be followed by a “b”.
“Colonia,” capitalized, is the name in Spanish for Cologne, Germany. Uncapitalized, it means “colony.” So using this form, rather than the latinized one, could cause confusion.
Not sure what you mean, but a country or land ending in a masculine is rather odd in latin. Usually (if not all of time) lands are feminine even if named after a male person e.g. roma, patria, america (named after one Amerigo or Americus), hispanola. The i before the a seems to be very popular with place names if it flowed well with the word. Same thing for other word named after males to describe feminine things like carolinian, shavian (Shaw), julian, georgia ect.
Simplest case: The name is already a name used by the ancient Romans, or a variation thereof. For instance, Claudia = Claudia, or Mark = Marcus.
Next-simplest case: Find someone famous with your name, and do it the same way they did. Example, Charles = Carolus. Saint names can be a good source, here, since they all have a standard Latin form.
And if that doesn’t work: Make it up yourself, making sure that it ends in -us for a male name or -a for a female, and follows a few other miscellaneous patterns for Latin words.
As for why, it looks cool, and important, and official, and all those things.