The following meaning of Extra is taken from Oxford Advanced Dictionary.

Adjective? Extra; Extra; Additional:?

Extraordinary; In particular; Extraordinary; special

Noun (short for noun)? Extra things; Something that is charged separately.

Extra on the bottle is a double part of speech: adjective or adverb. It should be understood as "special taste" or "super cool experience"

Wrigey's is the registered trademark of this chewing gum, namely: Wrigley, William Jr.: (1861-1932) American manufacturer. He founded William White Jr., the largest chewing gum manufacturing company in the world, at 189 1.

If there are English words, they are words with different tastes, such as apples, pineapples, bananas and oranges.