septillion:
If it's already written for an OLED (which sound like micro controller / Arduino to me) why do you need to convert it?If you want to convert it from another micro / IDE I would suggest to convert it to UTF-8 because that's what the IDE supports and libraries that use more then plain (extended) ASCII will most likely use UTF-8 as well.
Thanks.
westfw:
Arduino does not have any built-in support for Unicode or other wide strings.
Strcat might still work, with a lot title casting, if there are no embedded nulls.
Thanks.