No fallback on export when EN translation does not exist

[PierreAnctil]

In the UI

• when there is no FR (or other language) translation, EN is the fallback
• when there is no EN translation, FR (or other language) is the fallback

In the exported files

• when there is no FR (or other language) translation, EN is the fallback
• when there is no EN translation, there is no fallback

@worldskills/geeks is this on purpose since FR translation is needed for the user to be able to provide EN translation in the UI whereas exports only displays translations? Or should it be fixed?

cc @Simon-Woirgard @ailtisWSFR