"Would you teach me Mandarin?" should be spoken as (in standrad mandarin, I think all Chinese should understand.)

knee "chee owl" wall, wall yee, cur yee ma

1) "chee owl" quiken the speak of the 2 words as like merging them into one.
2) the first "wall", drop the phoenitical effect of LL, you stop immediately before you are about to say the LL
3) cur, like curse without se phonetically. That is the curse become cur (or cur in curtesy)
4) ma should pronouce like ma in "Mars", drop the "rs", only the ma should be pronounced. Sort of pronouncing the word "mother" without the "ther"

HTH

IMOH, unless one learn Chinese or learn to speak in Mandarin at age 1 to 12, I don't see any chance to pick up the langauge later than 12.