I'm not sure which dialogue you mean so I'll just go over all of them. Hopefully I've not made any mistakes, but I'm pretty sure this accounts for all the text:
First of all, each route down to this field screen has an assigned number which is pushed to a character-specific variable (called 'LastCloud [13][84], LastBarret [13][85], etc, in Makou's default variable naming):
Right Path #1
Left-Up #2
Left-Down #3
This determines which exit the characters will emerge from on Field 4_1.
Which character appears and speaks from the other exits (if applicable)
triggers from Group 12 - l2, and runs Script 3 of Group 0.
First thing it does is check what route Cloud took (1, 2, or 3) to run one
of three branches. Next is character priority in ascending order:
Tifa
Barret
Cid
Red XIII
Cait Sith
Yuffie
Vincent
Tifa will always appear and speak if she was sent down a route, while Vincent
must be sent down a route alone to be seen. When it's determined who is going
to appear, it triggers their related script (depending on the exit), scrolls to them,
and triggers their dialogue line, playing Script 3 for the associated character
(to animate them coming out of the exit).
Now onto Group 17 - Modo. This handles Cloud not being able to double-back
through the Left-Down Path if the following two conditions are met:
-) He emerged from either of the other two exits/picked the other routes
-) At least one party member went through the Left-Down route
Modo's first bit of script is it's Init, where it checks the Game Moment and
then each character's chosen route twice. It checks twice because this branch
performs two functions.
First, it pushes the character's 'ID' into a temporary variable if they were sent
through the Left-Down path. Note that if Cloud used the Left-Down path then the
location is 'cleared' and Cloud can leave to back-track through Left-Down path.
[5][28] will also be left at 0 in this case, keeping the walkmesh triangle active.
One thing to note is that it's ascending order again (as above). If Tifa was
sent through the Left-Down path then the [5][28] is given her number (2) and
the script jumps to label 8 to perform the second task of this branch; counting
how many party members were sent through the Left-Down path and placing
the value into the variable [5][29].
With the Init of Modo done, now when you trigger this location it'll run Script 6
of Cloud (unless it's been cleared as mentioned before) who will make one of two
variations of a remark:
'Where is [NAME]?'
'Where is [NAME] and the others?'
[5][29] was counting before. If it equals '1', then the singular will be used. If
it doesn't equal 1, then it must equal 2 or higher and so the other version will
be used to cover the other party members. Only way for it to equal 0 is if no-one
was sent this route.
And finally, the item box dialogue is triggered when talking to it