Can`t say for Sickle, but in Sentinels you need to create a special excel file that contains phrases of the dialogue. This file should be imported into the mapedit in 'dialogues' tab.
Before importing the file you need to create a person (persons - if you have several partisipants in the dialogue) in 'dialogue-pers' tab that will match your file`s person name. You can pick any of the available ones if you wish.
Here is an example of the dialogue file that occurs in APN mod once you report to the major at base: http://www.lordsofth...e_after_m01.xls