The layout box needs one frontmatter field called lang. Who writes it is none of its concern.
Without a further plugin
A site with a handful of translated pages manages without one:
---
title: Über uns
lang: de
---From there byLang.de applies. That is enough for a bilingual start page or an imprint in two
versions.
With quartz-multilanguage
As soon as whole language trees are involved, maintaining the field by hand becomes tedious. Then
quartz-multilanguage sets it itself — from the
folder name (en/…), from a file suffix (note.en.md) or from the frontmatter. It also brings the
language switcher this site carries at the top right.
For the layout box nothing changes: it still reads only lang.
Order matters in one place
order decides when Quartz loads a plugin. The layout box is a pure component and reads the
frontmatter only when the page is built — by which time every transformer has long written whatever
it had to write.
So there is no order to observe here
Anyone using both plugins has nothing to set in
order. The value recommended for quartz-multilanguage (order: 65, aftercrawl-links) concerns its own work on the content, not its interplay with this box.
Two files instead of two entries
A common detour is to create one instance per language and keep them apart with display or
frontmatter. That works, but costs two entries, two frontmatterKeys and double the maintenance.
byLang exists for this.