Since you're going to need to rewrite file contents, start with the define-pages-editor as a base. The configuration tool is not a good model for reading the entire file.
Enhance its file-reading facility by adding line-parsing to identify each define statement.
Build input fields on the screen for each one
Collect all the info.
Validate the info, and write the defines back to the file.

If you want to rewrite the language infrastructure to use the database instead, keep in mind the need to support multiple languages and also to handle code upgrades. You'll still need to create a user interface to present and collect the information, then validate it and save it.