If you import a CSV string table from C++ (say, when your game module loads) these string tables are available in the Editor and Loc Dashboard gathers the text from them. They’re also monitored and reloaded instantly if you add something to them.
However, both the Editor and Loc Dashboard fail to load CSV string tables if there is a space in their paths. The irony here is that the default Unreal Engine project directory on Windows is C:\Users%username%\Documents\Unreal Projects… so… this is broken by default 
You can fix this by moving the CSV file to a path with no spaces: that helps and the Edtior and Loc Dashboard load the string table correctly. But in that case you lose the hot reload as you’re moving the CSV file outside of the monitored Conten directory.
So the only good way is to store projects with no spaces in paths.
Hint: if you want to use CSV string tables (text files you can easily edit and merge) instead of storing text in binary assets (I have no idea why UE built-in string tables are binary, there’s no reason for that), see this thread: https://answers.unrealengine.com/questions/757986/view.html