- each character will be two bytes (so, for example, char
      lookup table you may have allocated needs to be
      expanded from 256 to 256 x 256 = 65536 elements)
    - that you would need to use wide char types (wchar_t
      instead of char)
    - that you would need to use wide string functions (like
      wprintf instead of printf)

Unicode support involves more than just the minimum number of bits used per character.

Say you're writing a method to truncate a string to a certain length. What if your text contains a code point outside the basic multilingual plane, and each character can't be represented in just 16 bits? If you truncate in the middle of a character, the result will be an invalid string. What about combining characters? If you truncate in the middle of a combining character sequence, you'll end up with half-formed output (e.g., letters missing a diacritic). If you work with text, you should know this stuff!