Has your language key line breaks or only the translated string? If so, I would remove it from the key and only translate the string. Usually, because of laziness, in the English version of my language file the key and the translation is the same. But in this case I would use a key without line breaks.
This works exactly as it should. Usually, the English key and English translations in my file are the same. But in this case I decided to shorten the key to baseTwo because the key has to match exactly, otherwise it doesn't work. With multiline strings as key this is too error prone. That's why I asked.
Where I can't get it to work is in SwiftUI preview canvas. But in the app itself it's fine.
In the Localizable.strings you don't use the syntax of Swift mulitline strings.