Yes, it's a problem with the keyboard configuration. For instance, if I press Shift + "-" (which generates an underscore), it'll write an interrogation mark. SRB2 uses the NA keyboard system, as stated above. You have to press other keys to get the characters you wish. IIRC, [ and ] are the 2 keys between P and Return (Enter).
More complicated characters such as accented, or Cyrillic characters are never going to happen because they'd have to fit (and be legible) within a 7x7 square.