The intermediate build stages' own cleanup only matches single-character
extensions (a `*.[po,mo]`-style glob), so `.po` source files can still be
present when copied into a custom image. Strip them explicitly in the
documented recipe so it does what the comment says.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
BUILD_TRANSLATIONS only takes effect when building the image from
source; extending an already-published tag in a small downstream
Dockerfile (the pattern already documented on this page) can't add
translations after the fact, since non-English files are already
stripped out of the published layers. That distinction wasn't
documented anywhere, and came up repeatedly in #35959 as real user
confusion after 5.0.0 made translations opt-in.
Documents the working multi-stage COPY --from pattern a community
member worked out in that issue for pulling the compiled translation
files out of the superset-node/python-translation-compiler build
stages, and clarifies the BUILD_TRANSLATIONS ARG description to point
at it.
