Reading aloud dual language text (or text in multiple languages)

At this time we don’t have language switching for reading aloud in @Voice app. However if you have an Android 8 or higher device, you could use Google TTS “Language detection” feature for this. You can enable "Conservative" or “Aggressive” language detection in Google TTS settings (under Android system settings – Languages & input – Advanced – Text to speech output – select Google TTS as the “preferred engine” and press gear icon next to it. There is “Language detection” setting there.
 
Next in @Voice app, press the round button with up arrow near bottom-right, then press the “Change voice or language” button, and set “Use only the system default voice”, as otherwise the language detection does not work in Google TTS. It’s not perfect though, they still have bugs and problems detecting the correct language sometimes. Also I find the "Aggressive" setting a little bit... too aggressive. For example in Polish text it switched to English voice when one English sounding person name was mentioned.