As in, where it appears in Frictional Games' code? Of course! Most are probably located in OnStart(); however some change later on in the map. Here's an example from theta_exit.hps, where they have two instances of changing the SetText.
void OnStart()
{
//Unrelated Code Here
//
//////Level Audio and Preloads
Sound_PreloadProject("02_07_theta_exit_a");
Sound_PreloadGroup("Flashback/Level/02_07", true);
LastOnSoma_SetText("02_07_theta_exit_1");
}
void SequenceWakeup(const tString& in asName)
{
//There is lots of code here for this sequence. Good job FG! o.0
//This particular part seems to be when you detach from the wall.
Player_SetFlashlightDisabled(false);
LastOnSoma_SetText("02_07_theta_exit_2");
}
As we can see here, in the first instance, the LastOnSoma_SetText(); string is changed to become an entry called "02_07_theta_exit_1" when entering the map. Which would be located in the config/english.lang file. And sure enough, it is. (Spoilered and removing other entries for obvious reasons).
I've included the second instance it changes also because it appears that you can change it at any time. Handy!
In a way, it is a global variable, since such text is stored in memory within the save. It is setting the string to display when you hit continue or load game. Here's another example from earlier on in the game (pardon the twitch chat. Sourced from Kreekakon's stream).
This particular string appears in the english.lang file, with this entry.
And... well, that's how that particular thing works. The value is saved in memory whenever the game autosaves or the player presses Save and Exit, and is then set for when the Player returns to the game should they need a reminder of where they are.