Download and install the Official 7-Zip Utility (Windows) or The Unarchiver (macOS).
Ensure you are using the 7-Zip tool specifically; standard Windows "Zip" folders often cannot read the .7z format. DLG18.7z
If this is a dialogue archive for a game (common in modding communities), you will see .txt , .json , or .xml files. These are typically placed in a game's "Lang" or "Script" folder to update in-game text. Download and install the Official 7-Zip Utility (Windows)
Look for a README.txt or install.txt file inside. These files contain specific instructions from the creator on how to use the "DLG18" assets. Troubleshooting you will see .txt