You may have seen people with vision impairment using screen readers for using phone. Such screen reader apps use Android's Accessibility API to get data from apps and read it out aloud. Similarly, Manglish app gets text from screen, converts and displays an overlay.
There is the possibility to misuse this power and see whatever is on your screen. Trust is very important here. Beware of apps using this.
ഫെഡറേറ്റഡ് സോഷ്യൽ വെബ്ബിലെ മലയാളിക്കൂട്ടം.