"Torg understands the klingon, Mara don't understand the Klingon."
Why wouldn't it be right?
"Mara" is one person, so you need the singular form "(she) doesn't".
"don't" is used when the subject is plural, e.g. "they don't".
"doesn't" is from "does not" and has the -s for "he, she, it". "don't" is from "do not" and does not have the -s.
Silly me. I should brush up my English instead.
I always feel a little badly marking suggestions incorrect when the person obviously understands the Klingon just fine, but has translated into imperfect English.
One of the unfortunate shortcomings of using a machine that relies on a pre-filled list of acceptable responses rather than having a human teacher who actually understands both languages.