When you click the ellipsis button in the property cell value for the Font property, the Windows font dialog appears and you can find the Charset setting in it. An alternative way is to set the Charset property in code.
However, all this may make sense only if you are using an outdated version of iGrid like the v2.51. The latest versions of iGrid implement a new cell editor based on the Unicode edit control and your problem may go away simply by switching to the latest version. Try it.