Why this cannot be "Jenta spiser et svat pepper" ?
Because 'pepper' is an uncountable noun, so you can't count 'one pepper', just like you can't count 'one salt'.
that's make sense! Sorry for stupid question >.<
I've edited my reply as I realized my mistake...
Wait, how so is pepper plural? If it is plural, then would not it be correct "Jenta spiser svartE pepperE"?
I've correct my comment. The plural of 'pepper' is either 'peppere' or 'peprer', so your suggestion would be correct.
Who's been spying on me?