From the iOS Speechify app, open a file in your library.
On the listening screen, at the bottom left, tap on the "human" icon.
Then, choose the voice/language of your choice (the Voices with "Premium" words next to them are Premium High-Quality Voices)
Note: Speechify will be able to read in any of the languages listed. Say you have a text written in Italian - if the Italian language is selected, it will read in Italian. If you use the Italian voice to read texts written in English, the app will read in English using the Italian voice/accent.