Add LANG environment and /usr/lib/locale

sdks/java/container/Dockerfile-distroless

@@ -25,6 +25,8 @@ ARG BEAM_BASE
 ARG DISTROLESS_BASE
 FROM ${BEAM_BASE} AS base
 ARG TARGETARCH
+ENV LANG C.UTF-8
+
 LABEL Author="Apache Beam <[email protected]>"
 
 RUN if [ -z "${TARGETARCH}" ]; then echo "fatal: TARGETARCH not set; run as docker buildx build or use --build-arg=TARGETARCH=amd64|arm64" >&2; exit 1; fi
@@ -33,4 +35,8 @@ FROM ${DISTROLESS_BASE}:latest-${TARGETARCH} AS distroless
 
 COPY --from=base /opt /opt
 
+# Along with the LANG environment variable above, prevents internally discovered failing bugs related to Dataflow Flex
+# template character encodings.
+COPY --from=base /usr/lib/locale /usr/lib/locale
+
 ENTRYPOINT ["/opt/apache/beam/boot"]