Wir werden den Terrorismus nie unterstützen.

This is translated “We will never countenance terrorism.”

The word “countenance” in English is archaic; it’s almost never used in casual speech and is uncommon to hear even in formal settings (usually mostly in church or old literature), and even there the verb form of it is even more rare.

Perhaps this could have a more modern translation? “We will never back terrorism.” or “We will never support terrorism.” seem the most natural translations to me.