Why does don Saporita and the Spanish speak with a lisp? Is he OK? isn't it weird for people to choose to speak with a listp? Yes, don Saporita is OK; and no, to the Spanish, the lisp is as common as our "th".
The myth of the lisping king is the theory of why the Spanish would pronounce "z" and "ç" like an English "th". Legend has it that Rey Felipe II (1556-1598) was a kind and popular king, but he had a lisp; and in order to pay respect their king the Spanish began to mimic this lisp and incorporate it in their daily speech.
However, this legend has been falisified by evidence that a lisp would provide the English "th" sound to /s/ as well as /z/ and /ç/. For example, in modern Spanish we pronounce a word like "delicioso" (day - lith - i - oh - so) not (day - lith - i - oh - tho).
The use of the English "th" in cases of the Spanish /z/ and /ç/ probably comes from a need to differentiate between the /s/ sound and the /ç/ sounds when speaking. This theory would be supported by the reasons we use accents in Spanish, especially with words like "HAblo" and "HablÓ", where the mere sound of the word changes the meaning completely.
Reference:
Pharies, David. La breve historia de la lengua espanola. Chicago y Londres: The University of Chicago Press, 2007. 154. Print
