I am not sure if BA has such a set up. I have met some SIN-based crew members on SIN flights but they only have a limited presence (ie the flight wouldn't be crewed entirely by the SIN base) - there were usually 2 on every flight, who'd do the Chinese announcements and presumably assist Chinese speaking pax. I was always under the impression that virtually everyone speaks English in SIN though???

QF has a LHR base which operates LHR-Asia. The Australia-based crew members operate the Asia-Australia bits of the LHR routes and all other long haul segments, including all of the FRA route.