So I was curious.......never really thought about this scenario. I exported a FTVSE screen (English-US) and reviewed the XML. I didn't see anything in there that appeared to identify the default language. It only contained the text for the language that was currently active when I performed the export.
I created a new application using a different default language (English-AU). Then I imported the screen into that application. The text appeared. So it would appear that there is nothing connecting the display to a specific language. And, the exported file would only contain the text for the current language at the time of the export.
If I had five languages, it would appear that I would have to export and then import, then change the language and repeat for each additional language. I could certainly use the language tools to export the entire application to an Excel file and make the modifications there. That is clumsy, but probably the best solution if there are several languages.
Back to the original poster's dilemma.....if the screen in question was exported, then all that should be needed is to import it. The languages of the source and destination applications do not appear to be relevant.
However......if you instead used the "Add Component Into Application..." option to add the display, the source and destination languages are maintained. I used that option to add my English-US application display to my English-AU application. I got all question marks.
This is what it sounds like has happened in your case. You really don't want to do language switching for just this one display. Instead, open the source application and export the display. Then take that export and use it to import into the destination application.
OG