Append default Sphinx configurations for Chinese and Japanaese

Automatically select `xelatex` for Chinese and `platex` for Japanese.
These defaults can be overridden by the user.

Force `latex_use_xindy=False` for now until we support it in our
Docker image.

Author: humitos

readthedocs/doc_builder/backends/sphinx.py

@@ -153,6 +153,9 @@ def get_config_params(self):
             'dont_overwrite_sphinx_context': self.project.has_feature(
                 Feature.DONT_OVERWRITE_SPHINX_CONTEXT,
             ),
+            'use_pdf_latexmk': self.project.has_feature(
+                Feature.USE_PDF_LATEXMK,
+            ),
         }
 
         finalize_sphinx_context_data.send(

readthedocs/doc_builder/templates/doc_builder/conf.py.tmpl

@@ -140,3 +140,38 @@ if 'extensions' in globals():
     extensions.insert(0, "readthedocs_ext.readthedocs")
 else:
     extensions = ["readthedocs_ext.readthedocs"]
+
+{% if use_pdf_latexmk %}
+project_language = '{{ project.language }}'
+
+# User's Sphinx configurations
+language_user = globals().get('language', None)
+latex_engine_user = globals().get('latex_engine', None)
+latex_elements_user = globals().get('latex_elements', None)
+
+chinese = any([
+    language_user in ('zh_CN', 'zh_TW'),
+    project_language in ('zh_CN', 'zh_TW'),
+])
+
+japanase = any([
+    language_user == 'ja',
+    project_language == 'ja',
+])
+
+if chinese:
+    latex_engine = latex_engine_user or 'xelatex'
+
+    # Remove this once xindy gets installed in Docker image and XINDYOPS
+    # env variable is supported
+    # https://github.com/rtfd/readthedocs-docker-images/pull/98
+    latex_use_xindy = False
+
+    latex_elements_rtd = {
+        'preamble': '\\usepackage[UTF8]{ctex}\n',
+    }
+    latex_elements = latex_elements_user or latex_elements_rtd
+elif japanase:
+    latex_engine = latex_engine_user or 'platex'
+    latex_use_xindy = False
+{% endif %}