Anlaşılabilmekteysem çok daha yavaş konuşmalıysın
If you want me to understand you, then you must speak more slowly

bod your words are growing every day,

I think you should say:
seni anlamamı istersen- if you want me to understand you
or:
anlaşılabilmek istersen- if you want to be understood (it doesn't sound very polite though)

anla-şıl-abil-mekte-y-se-m

Verb stem + passive mood + potential mood + mekte present + buffer consonant + conditional modifier + first person singular of "to be"

Because -mekte sounds better with -şil

good point