I think that your question has been answered in
Eva's post and my post, but I will compile the informations
A) In Spanish
X and J are not interchargeable and are not pronounced the same way.
J is pronounced as [kh]
X is pronounced as [ks] (axioma) or usually as [s] at beginning of word (xilofono).
In old ages, in Spanish, X was pronounced as [sh] (just as nowadays in Basque or Catalan) -nowadays this pronunciation is conserved in some Spanish dialects, but it is not the standard pronunciation, only dialectal, and in some Nahuatl and Mayan names-. Then, the sound evolved to [kh] (XVII century), and after the publication of Real Academia Española rules (1815, in its 8th edition) this sound is
only spelled with J, not with X. Exceptions: some surnames (not first names) as Ximénez (also spelled Jiménez and Giménez) or Mexías (also spelled Mejías) and some place names as Oaxaca, México (or Méjico, both forms are correct in Spanish) and Texas (or Tejas, both forms are correct in Spanish).
b) The
only correct form of the name in Spanish is
Javier.
Xavier can be the English, the Catalan or the French form, but not the Spanish form.
c) The words beginning with X (30, more or less) in Spanish are from Greek origin.
d) X is considered a Spanish letter and it is present in words from Latin origin (excusar, excursión) or Greek origin (xilofono). It is very usual because the prefix ex- is very useful (excarcelar, expatriar...) and the preposition ex, too (ex marido, ex ministro...). Some other useful prefixes have the X, as extra.
e) In Basque, X has a sound [sh]. Usually, Basque words and names with X ([sh]) are adapted in Spanish as CH ([ch]): chatarra. But
Xabier was incorporated to Spanish before the evolution of X [sh] to X [kh] (and after to J [kh]), then the name experimented the same evolution of other Spanish names or words.
f) The use of
Xavier among Spanish speaking people or Hispanic people is for English form influence (they use the English form) or for a misunderstanding (or unknowledge) of the Spanish spelling rules (they think that X and J have the same sound) (and they commit a misspelling).
Lumia
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