Root cause: zh/msg.txt was a JSON blob (not key:value lines),
en/jp/ko msg.txt didn't exist, and sage_datamart wasn't in
sage/build.sh module list for merge_i18n.py.
Fixes:
- zh/msg.txt: JSON blob → key: value lines (24 entries)
- en/msg.txt: Chinese keys → English values (24 entries)
- jp/msg.txt: Chinese keys → Japanese values (24 entries)
- ko/msg.txt: Chinese keys → Korean values (24 entries)
- Also added sage_datamart to sage/build.sh module list
