I don't know the rule of FA language qualifier, but I do agree, in general the UA FAs doing a less than competent job on safety/general announcement (especially in Mandarin/Cantonese). The issue I found is it seems they don't have a standard script to follow when doing safety/boarding announcement, it feels like they make it up as it goes. Every flights I was on (mainly 895/896), the safety announcement was a bit different.