When you test your game using F6 (which opens Play Solo in a new Studio instance), nothing related to localization will be loaded at all.
This is an example of a key that we have had in the game for ages, just not loading. The rest of the UI has text that doesn’t go through any key.
But it displays just fine in normal Play Solo (F5)
This is also an issue when trying to test out different languages using the built-in Localization tools. You can only do that when you go through F5 play solo.