I work with multilingual text processing applications, and I strongly support that concept. A guideline of "use UTF8 or die" works well and avoids lots of headaches - it is the most efficient encoding for in-memory use (unless you work mostly with Asian charsets where UTF16 has a size advantage) and it is compatible with all legal data, so it's quite effective to have a policy that 100% of your functions/API/datastructures/databases pass only UTF8 data, and when other encodings are needed (e.g. file import/export) then at the very edge of your application the data is converted to that something else.

Having a mix of encodings is a time bomb that sooner or later blows up as nasty bugs.