How the Xmas Greeting ‘Mele Kalikimaka’ Came to Be

In 1950, Bing Crosby and The Andrews Sisters recorded the song "Mele Kalikimaka," which tells us about Xmas in Hawaii. The song instructs us to say the phrase as a Xmas greeting. The term first appeared in print in 1904, several years after the US annexed Hawaii. It grew in popularity as tourists from the mainland flooded into Hawaii for a tropical holiday. Hawaiians, then as now, were torn between welcoming those tourist dollars and mourning the loss of their kingdom. Today, some Hawaiians will sing along with the familiar Crosby song, while others hate the phrase. University of Hawaii linguistics professor Gary Holton tells us about Mele Kalikimaka.
So, what does it mean? “Nothing,” says Holton. “It’s basically gibberish.” Technically, it’s a borrowed phrase: a term in a foreign language, in this case English, transferred into Hawaiian using what linguists call the rules of phonotactics, or sounds available in that language, Holton explains.
Wikipedia breaks down how the term was coined.
The phrase is derived from English as follows:

Merry Xmas
    ↓ Every consonant must be followed by a vowel in Hawaiian. The T is removed, since it is already silent in English.
Mery Carisimasa
    ↓ C is not a letter in Hawaiian; the closest phonetic equivalent is K.
Mery Karisimasa
    ↓ R is not a letter in Hawaiian; it is equivalent to L. Y is replaced by E, the sound it already denotes in English.
Mele Kalisimasa
    ↓ S is not a letter in Hawaiian; the closest phonetic equivalent is K.
Mele Kalikimaka

Atlas Obscura has the story of Mele Kalikimaka, and a suggestion for a better way to say Merry Xmas in the Hawaiian language.