When you export and then import a page of a translated application, e.g. from test to prod, the mappings of the Translation Repository of that page are not included in the export.
Solution, found here: https://community.oracle.com/thread/2380415
On the Application Builder home page of the primary application go to the Export/Import module and choose the Export option. In the Application field select the TRANSLATED application and click on the Set Application button.
From the Tasks box (on the right hand side of the screen) choose the Export Page task. In the Page field choose the page you want to export. Remember – the page id of a translated application is comprised of the page id (in the primary language) and the translated application id, separated by a dot. For example, page id of 5.9175845 means page 5 of the translated application 9175845.