>> Ar nach brat berar do aés sétrenil cotnimtét demon eret nádˇnegar.
I'll try this.
Because any cloak which is brought from lustful (?) folk, a devil
accompanies it as long as it is not washed.
Ar -- preposition with several translations "for, since, seeing that...because
of...by means of, with regard to...etc."
nach -- form of 'nech' "any, whatever, some"
berar -- relative singular indicative present form of 'berid'
do -- confusion for 'de/di'
sétrenil -- see Dennis King's note earlier in this thread
cotnimtét -- looks like a form of con-imthet (accompanies) with a 3rd person
masculine class B infixed pronoun 'tn'
eret -- form of "airet..length, interval, space of time" The DIL entry for this
word quotes our source B and translates 'so long as it is not washed'.
nádˇnegar -- negative particle 'na' plus 'negar' passive present singular
of 'nigid' (washes)