Custom preprocess_function does not fetch translated value of the content type
You can confirm this by looking under the "Overview" tab of the translation interface:



If the percentage in the "Node types" for your second language is ("Norwegian Bokmål" in the image above) is 0%, the translated strings for the Node types has not been imported into the translation interface.  This means that even after you enable that language, the fallback English strings will be used.

However, it should now be possible to add these translation by hand.  Navigate to the translate tab of the translation interface, and limit search to Node types.



The strikethrough over the string with the two letters in the Languages column means that the translation is missing.  Click "edit" to add the missing translation.

This exact procedure fixed it for me as can be seen from the "Overview" tab below.  The percentage for "Node types" for "Norwegian Bokmål" in now 100%.