The English translation makes a common mistake. It should be 'more slowly' not 'slower'. Speak is a verb and cannot be modified by an adjective. 'Slower' is the comparative form of the adjective 'slow'.
Duolingo accepts both answers
Using 'a charaid' in all these phrases. Is it idiomatic, like using 'mate' or 'pal' - or is it as contrived as using 'friend' would be in English (makes me think of elves in tolkien).
It's pretty common in SG.
I like how the Speaker says... this... very... slowly.