Custom label doesn't show

Hello experts,

I have created (with extension) a custom language and in this language a custom label (as explained here). The way I created the label is one for the base language "en-us" and one (with the same ID) in the language I need translation. Then to test it I changed the label of a display menu item to my custom one and the translation doesn't show. It only shows the text in the "en-us" label but not the translation even when I change the language from the User settings menu. I guess I am missing something but I can't figure out what it is. Can anyone help?

Thanks