IDLMac

If you use a Unicode encoding in the Terminal you might encounter problems in IDL when sending commands after correcting wrong input that had contained a 'umlaut' (äöü) character or other non-English characters.

E.g. writing
[@ürint, 'He@]
...correcting it to...
[@print, 'Hello World!'@]
...and then sending it off, you will get
[@% Attempt to call undefined procedure/function: 'CPRINT'.@]

That is (I think) because Unicode uses two-byte characters and when deleting a two-byte character like an 'ü' IDL only deletes one of these two and the other one remains. This does not occur when you select a one-byte encoding like "Western European (Mac OS Latin)".