Luc,
Please try this: first start the text input (click to the plan), then change to chinese input language. After clicking chinese in the menubar, don't touch the mouse anymore. It seems that moving the mouse will reset the input language and wash away the input window.
Alternatively, select input language before starting ArchiCAD.
Hope it helps,
Greg
Mac OS X.3 / ArchiCAD 8.1
Gergely Kmethy
VP, Customer Success, Graphisoft