Two skills are required here, quick translation skills (far from easy) and public speaking (does not come easily to many people).

I have often found that it is far easier to critique the quality of of someone else's translation compared to when you have to do the translation yourself. It is just one of those things - there is a lot more pressure on brain processing. Being able to speak a language does not mean being good at instant or quick translation. Most people do not get this.

Cabin salaries are not the best in the world and HKG/SIN based crew will be paid less than UK counterparts. As as, the pool of people with who are really good with both these skills whose willing to work are cabin crew are limited.

Not sure if BA gets first pick of the recruitment pool either since other local airlines would have much better travel benefits (they fly to more locations) to offer. I often wonder if BA recruitment prioritises their English skills so they can understand the CSD and their fellow crew members.