The LPI examiners are aware that writing in perfectt English idiom is not an easy task for students whom English is a second or third language.
I think that "whom" should be replaced by "whose". What do you guys think?
Hello Adios (por así decirlo),
Unfortunately the sentence isn't entirely grammatical or idiomatic as it stands. It should be:
1. The LPI examiners are aware that writing perfectly idiomatic English is not an easy task for students for whom English is a second or third language.
Your suggested version (with "whose") is ingenious and not incorrect; though it would probably sound a little awkward to most native speakers.
All the best,