Phrase Syntax 
The many phrase variable names in vBulletin have their values stored as strings when the vBulletin cached language data is generated or regenerated.

For example, the phrase variable show_all_users is stored as Show All Users, and additional_options is stored as Additional Options.

Sometimes the strings contain substitution variables that are not replaced with specific values until runtime.

For example, the phrase variable showing_avatars_x_to_y_of_z is stored as the following string with substitution variables {1}, {2}, and {3}:
Showing Avatars {1} to {2} of {3}
At runtime, the string might contain the values 10, 20, and 24 in place of {2}, and {3}:

Showing Avatars 10 to 20 of 24.

Suppose you wanted the output string to look like the following:

24 Avatars Total. Displaying 10 - 20.

You could accomplish that by changing the string to the following:
{3} Avatars Total. Displaying {1} - {2}.
As you can see, the order of the substitution variables can be changed. The important thing is that you reference the correct substitution variable number for the output variable you want.
User Contributed Notes: Phrase Syntax