Setup locales so make mnuconfig works properly inside the dev container ; add nano to the dev container so git has a valid editor in case users use git directly within the container

.devcontainer/Dockerfile

@@ -1,9 +1,13 @@
 FROM zmkfirmware/zephyr-west-action-arm
 
+ENV LC_ALL=C
+
 RUN apt-get -y update && \
     apt-get -y upgrade && \
     apt-get install --no-install-recommends -y \
     ssh \
+    nano \
+    locales \
     gpg && \
     rm -rf /var/lib/apt/lists/*