Gcalctool does not properly support unicode characters. The problems are:
- GTK+ uses locale dependant strings so users can enter any unicode character  (normally UTF-8)
- The thousands separators and radix can be non-ASCII
- The internal representation is ASCII (the code assumes string[3] will be the third character which is not correct if the input is UTF-8)
- The flex parser is 8 bit only and freaks out when it sees UTF-8 characters. It doesn't appear the standard upstream version of flex can support 32bit strings.

The proposal is:
- Use an internal unicode (32 bit strings) representation 
- Convert GTK+ input to unicode
- Convert equation to ASCII before sending to the parser. Obvious substitutions such as ×->*, ÷->/ need to be made before parsing.
- Consider doing localization at the latest possible point, i.e. before sending to the GUI for display.

The factors making this difficult currently:
- Lots of code modified v->expression in various ways
- Lots of code calls ui_set_display