In the current version of Notepad++ opening .sql files results in Notepad applying SQL syntax highlighting to it. I'd like Notepad++ to do the same for other extensions as well, is there some setting where I can define this?
When you open a file in notepad++ it will attempt to load syntax highlighting for the contents based on file extension.
If you use custom extension for one of the existing languages you can add the custom extension in Settings -> Styler Configurator. Select language and add the extension in "User extension" edit box. To add multiple extensions separate them using Space.
You then need to re-open your file to see the syntax highlighting applied.
You can also change syntax highlighting style by selecting a different language from language menu.
Find the langs.xml file (usually under C:\Users[username]\AppData\Roaming\Notepad++), open it with Notepad++, find the line that begins with
<Language name="sql" ext="sql" and add the extensions you want in the ext field, separating them with a space.
To do this for a user-defined language, look instead for userDefineLang.xml and edit
If you installed notepad++ in "portable"-mode, then the langs.xml and userDefineLangs.xml will be directly in the folder where notepad++ is located.