Apex has no option for exporting Dynamic Translations - you would expect that in the Component Export but alas.
Dynamic Translations are of course included when exporting the entire application, but sometimes you might want to export the translations separately. For instance when you use the translations in a package/view/etc using apex_lang.lang, while the application itself is being updated and not ready for export.
- Export the entire application
- Open the resulting SQL file in a text editor
- Keep the top part, up to and including the "Set Application ID" section
- Keep the bottom part, starting from the "post import process" section
- In between, keep the Dynamic Translation parts that you want to include
In the (4.2) example below, 2 Dynamic Translations are included: