"External employees drink more coffee."
Translation:Externe Mitarbeiter trinken mehr Kaffee.
No, when there's no article, the adjective has to indicate the plural with a -e. Then when you see "externe Mitarbeiter" you know it's plural because that's the only time you'd see a "-e" in front of a masculine noun. (A feminine noun will clue you in with its plural form: externe Frauen.)
It's when you have an article that the adjective can take an -en. An adjective ending in -en tells you that the article has changed from the nominative form. So: "die externen Mitarbeiter" but "die externe Frauen."
Which is why you need to learn your noun genders and plural forms.