eh, can't thing of great counterparts on english...
you know, when baby cries, it's something:
byääh...
eh...
english a would be in most cases same as ä.
on the other hand, when it's used as prefix of a word, english ppl pronounce it like our ö and american as our "ei" (which means the same as "no" in english...)

so, back to the city name.
j - translates to y
y - no counterpart in my mind currently...
v - v
ä - a
s - s
k - k (or just c)
l - l

so it turns out something like:
yyvaskyla

one thing I know though, german ppl turn it like:
jyvaeskylae

which is looking pretty awfull even to me.
after all, I've been living in this small town (in 10 top in finland's scale) for 2 years now and am ready to move out asap.
so, after that, no one needs to try to pronounce it anymore.
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