But what that must mean is that she's known by a slightly different name in Japan, as there is no strong "th" sound available in the Japanese language's alphabets to perform it correctly, so an S sound is put there instead. So what this would mean is that she is known as Aerith everywhere, but Japan.

However, the fact that Sony did the translation for FF7, and Square did the translation for Kingdom Hearts, definitely does say something. It does open the possibility for me that Square decided that everyone outside of Japan would put their tongue between their teeth when saying this character's name.