5. The operation apparatus according to claim 4 , wherein, when a notification of completion of an operation input of a predetermined setting condition via the setting condition input window in which the third character string is displayed in the different language or a notification of instruction of execution of a predetermined function relating to the setting item is accepted, the character string changing unit switches the character string in the different language back to the character string in a language before change.
4. The operation apparatus according to claim 1 , wherein, when a setting condition input window allowing input of a setting item corresponding to a setting item key in which the language of the first character string and the second character string is changed to a different language is displayed on the touch panel, the character string changing unit displays a third character string, which is displayed on the setting condition input window, after changing a language of the third character string to the same language as the first character string and the second character string.