vscode-nls | npm module to support externalization | Internationalization library

I am trying to understand the workflow presented in https://github.com/microsoft/vscode-extension-samples/tree/master/i18n-sample for localizing Visual Studio Code extensions.

I cannot figure out how the i18n directory gets created to begin with, as well as how the set of string keys in that directory get maintained over time.

There is one line in the README.md which says "You could have created this folder by hand, or you could have used the vscode-nls-dev tool to extract it."...how would one use vscode-nls-dev tool to extract it?

What I Understand

I understand that you can use vscode-nls, and wrap strings like this: localize("some.key", "My String") to pick up the localized version of that string at runtime.

I am pretty sure I understand that vscode-nls-dev is used at build time to substitute the content of files in the i18n directory into the transpiled JavaScript code, as well as creating files like out/extension.nls.ja.json

What is missing

Surely it is not expected that: for every file.ts file in your project you create an i18n/lang/out/file.i18n.json for every lang you support...and then keep the set of keys in that file up to date manually with every string change.

I am assuming that there is some process which automatically goes "are there any localize("key", "String") calls in file.ts for new keys not yet in file.i18n.json? If so, add those keys with some untranslated values". What is that process?