You don't need a separate text file:
[This is choice 1]
Hey, this is the text that will appear if the variable is 5!
[This is choice 2]
This will appear if the variable is 6!
[This is choice 3]
This will appear if the variable is 12!
---
Then in your event, you do a conditional branch for the variable being 5, call get_dialogue("This is choice 1"), another branch for 6, call get_dialogue("This is choice 2"), another for the variable being 12, call get_dialogue("This is choice 3").
You can also arrange your text files into folders in the Data folder, and then just include their directory in your string for the text file in languages:
:english => {
:dialogue_files => ["dialogue.txt", "chapter1/dialogue2.txt"] ,
:suffix => "EN",
},