When watching FMA Brotherhood, when van Hohenheim is talking to Pride, he refers to him as "プライド (Puraido) when he is talking to him by name, but when he is listing the seven deadly sins, he uses the term "傲慢", which is pronounced "ごうまん" (gouman). Is there any indication of why the character name is different from the term itself? This is probably true for all seven of the Homunculi, but I only noticed it specifically for Pride.
This is a simple "English is cooler"
As all the homunculi are named with the english seven deadly sins, their names are the hiragana/katagana representation to the english vocalization.
but when referring to the sin itself the correct translation ("傲慢") is used, as it is not a name (that also has to sound cool), but the thing itself.
I verified this is true to the other homunculi too, though not for "Father"