Adding custom language file to standard Fiori app

Hi all!

I'd like to ask how to make use of a custom translation file for a standard Fiori app. It's the Inbox app, if that's relevant.

I can download the UI code using /UI5/UI5_REPOSITORY_LOAD, create a new language file to i18n folder for the specified language, but then:

- Do I need upload the whole folder back to system or could I upload just the new file?

- If I upload the whole app, can I use the same name or should I do a custom version?

- I hope I don't need to do an extension just for the new language file?

Something else?

Thanks again!

br,

Ossi