The only real problem is conversion to Unicode. You should learn how Unicode support is implemented in Delphi – start from Marco Cantu White Paper: Delphi and Unicode
It is impossible to estimate the amount of work required to upgrade old applications to Unicode without knowing the actual code. If you were using string types in the standard way, the conversion would be easy. Any low-level tricks with string types (like storing binary data in strings) are now deprecated and the correspondent code should be rewritten.