The only way I know is to cut and paste from the log files. They are written continuously, so if you need some recent text, just be sure that this message category is logged and reopen the log file in an editor.
I know of users who have written text filters for Linux that monitor the log files, color code the message categories and display them in many different ways. You could e.g. display each message category (main chat, guild chat, group chat, tells etc.) in different windows or however you like.
I use extracts from the logfiles typically to document the quests I have finished.