I have to study English.
Because I lean Icelandic but the class is used English.
I sometimes can't understand what our teacher and classmates say.
I'm lonely because when they're laughing I can't understand why they're doing so. この表現は自然ですか？

Beacause I am learning Icelandic, but the class is taught in English.
Sometimes I can't understand what my teacher and classmates say.
It's lonely because when they're laughing, I can't understand why. /I can't understand what they are laughing about.