So, Which One was Older Again?: Teefa and Salah are twins, right? And they only call each other "my sister" since they are the same age. But since the Japanese culture places emphasis on where a person stands in family, they have no choice but to express it.
Salah calls Teefa "Ane" [姉] or "Neesan" [姉さん] while the one time Teefa says "sister" she simply says "Imouto" [妹]. From those words, they are essentially confirming that Teefa is the older sister, while Salah is the younger.
Blood, the Truth of a Seal: Remember Salah's use of "Royal Tears" to enter Stavery Tower? Well, not in the Japanese version. Originally, she used her blood instead [王家の血, lit. Blood of (the) Royal Family]. Considering blood is used by some fantasy sorcerers for power, and the power that is usually associated with a royal bloodline, this makes a lot more sense.
And speaking of blood, the Null Cards seem to have been initially called Blood Cards [血のカード].
Gee...There Goes the Red Cross: The triangles on Salah's hat and shield were initially crosses. Censorship of religious symbols in early SNES RPGs...color me shocked!
Is She Being Polite, or Hiding?: Salah calls Axs Ojisama [叔父様] in the Japanese version. It's generally used to mean uncle (the kanji showing one younger than a parent) or also an older gentleman, according to JWPce. It is interesting that she'd use such a term for her protector, though since she's a princess it's not exactly surprising that she's being polite to him. Though, there still is the possibility that she pretends to be his niece to hide herself from her enemies.
Chivalry is Dead...So Are Honorifics: Use of honorifics by characters in the game is pretty small. Besides Salah's nickname for Axs, the only other time a party member uses one is when Rooks calls Icorina, Icorina-obasan [イコリナおばさん]. Even Salah, who I'd expect to be the type to use honorifics for the entire party, doesn't do so.
The only other use of honorifics in the game are among Ariel's apprentices. They all use the -sama [様] suffix for him. Zerel also calls Rooks, "Rooks-dono" [ルークス殿] since they are both swordsmen. Ariel also uses an honorific in reference to Salah, but it's only -san, and not -sama as you'd expect a princess to be referred to.
She was Dying? When?: It seems that line about Salah dying in Chapter 2 was supposed to be a threat on Ariel's part about killing her if Rooks made a false move. I mean, he didn't need her 100%, seeing as he now knew where the Enchanted Jewel was hidden and they still had Teefa to break any royal seals, but she was a convenient captive at that moment so using her to keep the ever-kind Rooks at bay would definately be a good plan for him.