[v0.9.1] Add CN docs (#2657)

### What this PR does / why we need it?
Add CN docs
- backport #1870
- Add `make po`

TODO:
- Translation new doc

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
```
cd docs
python -m venv ./.venv
source .venv
# Install dependencies.
pip install -r requirements-docs.txt
# Build the docs.
make clean
make html

# Extract po files
make po

# Do translations

# Build the docs with translation
make intl

# Open the docs with your browser
python -m http.server -d _build/html/
```
http://localhost:8000/
http://localhost:8000/zh-cn

---------

Signed-off-by: aidoczh <[email protected]>
Signed-off-by: Yikun Jiang <[email protected]>
Co-authored-by: aidoczh <[email protected]>

Author: Yikun

docs/Makefile

@@ -19,3 +19,11 @@ help:
 %: Makefile
 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
 
+po:
+	make gettext
+	sphinx-intl update -p _build/gettext -l zh_CN
+
+intl:
+	sphinx-intl build
+	@$(SPHINXBUILD) -b html -D language=zh_CN "$(SOURCEDIR)" "$(BUILDDIR)/html/zh-cn" $(SPHINXOPTS) $(O)
+

docs/README.md

@@ -11,13 +11,19 @@ pip install -r requirements-docs.txt
 # Build the docs.
 make clean
 make html
-```
 
-## Open the docs with your browser
+# Extract po files
+make po
 
-```bash
+# Do translations
+
+# Build the docs with translation
+make intl
+
+# Open the docs with your browser
 python -m http.server -d _build/html/
 ```
 
-Launch your browser and open http://localhost:8000/.
-
+Launch your browser and open:
+- English version: http://localhost:8000
+- Chinese version: http://localhost:8000/zh_CN

docs/requirements-docs.txt

@@ -7,3 +7,4 @@ sphinx-togglebutton
 myst-parser
 msgspec
 sphinx-substitution-extensions
+sphinx-intl

docs/source/conf.py

@@ -86,8 +86,8 @@
 #
 # This is also used if you do content translation via gettext catalogs.
 # Usually you set "language" from the command line for these cases.
-language = 'en'
-
+locale_dirs = ['locale/']   
+gettext_compact = False   
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 # This pattern also affects html_static_path and html_extra_path.