Open the the games '/Teraurge/database' folder using File -> Open Folder.
Start by navigating to a characters diag.txt file, using the explorer menu (Ctrl+Shift+E) on the left-hand-side.
After a few moments, the validator will run and come back with a list of problems (Ctrl+Shift+M).
There are 3 main types:
VSCode should detect the language as 'tuscript', indicated in the bottom right of the screen. If this displays something else, such as 'Plain Text', click on it and select 'tuscript' from the dropdown menu.
The validator detects the "database" folder, and also folders that start with "database" e.g. "database_copy".
I've opened a dialogue file, and the language is set to 'tuscript', but no problems are displayed
Please double check that you have opened the '/Teraurge/database' folder and not just the '/Teraurge' folder.
This is especially important if you have multiple folders starting with 'database'.