Text for a key in a NEW level

[Mooserider]

Apologies, I'm not exactly sure what you mean - but if you've put the key in a lang file it would work for any level that the key is put in. If you mean making a key from one level opening a door in another, a callback in the level with the door should suffice
The callback for displaying a message is SetMessage("Category", "Entry", X.0f)
X being the amount of time you want the message to be on the screen.

Edit: Also in the future you should probably post questions like this in the development support section, just a tip