I just tried English<->Mandarin with my wife...though not always grammatically correct, it gets the point across.
For those who would use it while travelling abroad, keep it mind this requires an Internet connection. In China, you would need VPN since Google services are blocked.
WordLens works offline without any additional downloads, at least for the languages I tried (Spanish, French, English).
Audio translation and TTS works offline if you have the proper languages downloaded, but being able to detect what language is being spoken seems to be an online-only feature.
Baidu translate works great in China and will translate anything you copy to the clipboard automatically. Requires the usual insane Chinese app permissions so Xprivacy or something similar is a must.
For those who would use it while travelling abroad, keep it mind this requires an Internet connection. In China, you would need VPN since Google services are blocked.