From Original War Support Wiki
Tutorials -> Dialogs
Dialogs are when a character talks. There are several different types of dialogs:
Say, SayNoFace, SayNoName, ForceSay, ForceSayNoName, ForceSayNoFace, SayRadio, SayRadioNoName, SayEffect.
For each you first need to add what you want your character to say in your map's Texts.txt (or proper mission's .wri) file.
$ DMyUnitSpeech - Hello World!
A sound file with the same name as XX_MyUnitSpeech.wav (Where XX is the mission number. First character is replaced.) located in %MODDIR%\Sound\Dialogs\SIDE\XX\ (SIDE can be Am, Ar or Ru) will be played if it exists. You have to use sounds in WaveForm (.wav) container with PCM 22.050 kHz (or lower), 16 Bit, Mono.
The path where game will look for files is strongly connected with parameters you choose in Map Preferences dialog box so you have to set correctly the mission's number and campaign there (in Editor: File -> Map Preferences; third tab).
Next you need to add some code into sail to make a unit talk.
Saynoface is the same as Say except you don't see a portrait of the unit when it speaks.
Saynoname is the same as Say except you don't see the name of the unit when it speaks.
ForceSay is the same as Say except that it forces the unit to speak even if it is dying (but not dead).
SayRadio is the same as Say except that it does a radio effect over the portrait.
SayEffect is like say but doesn't require a unit reference.