Yes, it is possible to change the reply prefix in iNotes for all languages, along with other strings that may need to be changed for customisation purposes. These strings are stored as variables in the dwa_XX.properties file in the Forms85.nsf design under Resources -> Files (XX in this case is the two character representation of the language in use).
For example in the German properties file dwa_de.properties, to change the reply prefix from “Antwort: ” to “RE: ” the following variable should be changed from:
L_RE=Antwort:
to
L_RE=RE:
Then after the cache is cleared (or server is restarted) the changes will be noticeable in the iNotes interface.