When trying to use foreign fonts (i.e. euro symbol) in the Toad editor, it is not displayed correctly, showing up as other characters (i.e. double bars or boxes, etc).
When copy and pasting Cyrillic characters into the Editor they are turned into question marks. The characters can be typed into the Editor without problems, but if they are pasted in they turn into question marks.
Characters unsupported by the font setting for Toad's editor.
Go to View | Options | Editor | Behaviour - Languages "Editor Font". Select another font that does handled the characters needed (i.e. for the euro sign, Arial should work).
It may be necessary to restart Toad or reboot the computer if the change does not take affect.
Better UTF8 and characterset support is provided in Toad for Oracle 10.
If issues continue to occur in other windows and/or the data grid, check the Oracle client version. The noted font settings only applies to the Editor window.