You can use the Localization Dashboard to gather your text for translation.
There’s some information about it here, although it’s somewhat out-of-date now:
https://forums.unrealengine.com/development-discussion/content-creation/34379-localization-dashboard-preview-and-explanation-of-ue4-s-text-localization-process?63394-Localization-Dashboard-preview-and-explanation-of-UE4-s-text-localization-process=#post250553
The dashboard is enabled by default in newer versions, and comes with a default “Game” target. You’ll want to configure that to gather from your assets, add the languages you need, and run a gather.
This will give you your source text, which you can then export to PO to translate (something like PO edit might help here), before importing your translations and compiling them.
You also need to make sure the correct cultures are set to be packaged, as well as making sure your internationalisation support is set correctly (you can find these settings under Project Settings → Packaging).