Open the language window (IE using Common).
Type .roll with the lore choice following it.

This works for other skills too, but that's already fairly known. The new languages has been what's been stumping people I've noticed, as people have normally tried rolling the full names (lore: X) which only ever gets arcana.
The names you use for the skills are:
- Lore: Arcana - lore (.roll lore)
- Lore: Arch-Engineering - architecture (.roll architecture)
- Lore: Dungeoneering - dungeoneering (.roll dungeoneering)
- Lore: Geography and Astronomy - geography (.roll geography)
- Lore: History - history (.roll history)
- Lore: Local - local (.roll local)
- Lore: Nature - nature (.roll nature)
- Lore: Nobility & Royalty - nobility (.roll nobility)
- Lore: Religion - ???
- Lore: The Planes - theplanes (.roll theplanes)