Editora 0.18.3. Archived, so links from that release keep working. Read the 0.18.5 page →
Spell Check: Set Language…
spell.setLanguage Set the spell-check dictionary for this file.
How to run it
Open the command palette (M-x in the Emacs keymap) and search for Spell Check: Set Language…, then press Enter. It has no default keybinding, but you can bind one in Settings → Keymaps.