Can't get extra_english.lang to work

[Damascus]

I've followed all the tutorials and searched topics all over the forum but none of the proposed solutions seem to work. I'm starting out trying to use the .lang file to give a message when you attempt to open a door, and to rename an item.

First off, my files are arranged like this (I have the Steam version):
custom_stories/
|- Kassel/
| |- maps/
| | |- castle.hps
| | |- castle.map
| |- extra_english.lang
In my .lang file, I put the following:

Spoiler below!

<LANGUAGE>

<CATEGORY Name="Inventory">
<Entry Name="ItemDesc_StorageKey">A key to the storage room.</Entry>
<Entry Name="ItemName_StorageKey">Storage Key</Entry>
</CATEGORY>

<CATEGORY Name="Doors">
<Entry Name="castle_5">The latch is jammed.</Entry>
</CATEGORY>

</LANGUAGE>

And in my .hps file, I put the following:

Spoiler below!

void OnStart()
{
SetEntityPlayerInteractCallback("castle_5", "Message", true);
}

void Message(string &in asEntity)
{
SetMessage("Doors", "castle_5", 5.0f);
}

If I did everything correctly, when the player interacts with the door "castle_5," the script should bring up the message in the "Doors" category under "castle_5." And the key in question does have "StorageKey" for it's CutsomItemSubtypeName. Neither of them work properly.