Only detecting valid sentences?

[Kalle Karlsson]

I'm using Apache OpenNLP and I'm wondering if it is possible to train the 
sentence detector to only recognise valid (in some sense) sentences and 
discarding everything else? 
For example, let us say I have a document in english, but sprinkled inside that 
document there is sentences in another specific language and then I'd like to 
be able to detect only that other specific language? 
Is that possible with the sentence detector?
Thanks.