[FLINK-20422] Fix invalid links across languages

docs/_layouts/404_base.html

@@ -19,12 +19,13 @@
 specific language governing permissions and limitations
 under the License.
 -->
+{% capture index_link %}{% if page.language == "en" %}index.md{% else if page.language == "zh" %}index.zh.md{% endif %}{% endcapture %}
 
 <noscript>
-  <meta http-equiv="refresh" content="5; url={% link index.md %}">
+  <meta http-equiv="refresh" content="5; url={% link {{ index_link }} %}">
 </noscript>
 <script type="text/javascript">
-  var documentationRootUrl = "{% link index.md %}";
+  var documentationRootUrl = "{% link {{ index_link }} %}";
   var timeout = "5000";
   window.onload = function() {
     setTimeout(doRedirect, timeout);

docs/concepts/stateful-stream-processing.zh.md

@@ -308,7 +308,7 @@ A *DataSet* is treated internally as a stream of data. The concepts above thus
 apply to batch programs in the same way as well as they apply to streaming
 programs, with minor exceptions:
 
-  - [Fault tolerance for batch programs]({% link dev/task_failure_recovery.md %})
+  - [Fault tolerance for batch programs]({% link dev/task_failure_recovery.zh.md %})
     does not use checkpointing.  Recovery happens by fully replaying the
     streams.  That is possible, because inputs are bounded. This pushes the
     cost more towards the recovery, but makes the regular processing cheaper,

docs/dev/table/sql/gettingStarted.zh.md

@@ -86,7 +86,7 @@ It differs from a traditional database because Flink does not manage data at res
 
 Flink data processing pipelines begin with source tables. Source tables produce rows operated over during the query's execution; they are the tables referenced in the `FROM` clause of a query.  These could be Kafka topics, databases, filesystems, or any other system that Flink knows how to consume. 
 
-Tables can be defined through the SQL client or using environment config file. The SQL client support [SQL DDL commands]({% link dev/table/sql/index.md %}) similar to traditional SQL. Standard SQL DDL is used to [create]({% link dev/table/sql/create.md %}), [alter]({% link dev/table/sql/alter.md %}), [drop]({% link dev/table/sql/drop.md %}) tables. 
+Tables can be defined through the SQL client or using environment config file. The SQL client support [SQL DDL commands]({% link dev/table/sql/index.zh.md %}) similar to traditional SQL. Standard SQL DDL is used to [create]({% link dev/table/sql/create.zh.md %}), [alter]({% link dev/table/sql/alter.zh.md %}), [drop]({% link dev/table/sql/drop.zh.md %}) tables. 
 
 Flink has a support for different [connectors]({% link dev/table/connect.zh.md %}) and [formats]({%link dev/table/connectors/formats/index.zh.md %}) that can be used with tables. Following is an example to define a source table backed by a [CSV file]({%link dev/table/connectors/formats/csv.zh.md %}) with `emp_id`, `name`, `dept_id` as columns in a `CREATE` table statement.
 
@@ -156,12 +156,12 @@ In particular, Apache Flink's [user mailing list](https://flink.apache.org/commu
 
 ## Resources to Learn more
 
-* [SQL]({% link dev/table/sql/index.md %}): Supported operations and syntax for SQL.
-* [SQL Client]({% link dev/table/sqlClient.md %}): Play around with Flink SQL and submit a table program to a cluster without programming knowledge
-* [Concepts & Common API]({% link dev/table/common.md %}): Shared concepts and APIs of the Table API and SQL.
-* [Streaming Concepts]({% link dev/table/streaming/index.md %}): Streaming-specific documentation for the Table API or SQL such as configuration of time attributes and handling of updating results.
-* [Built-in Functions]({% link dev/table/functions/systemFunctions.md %}): Supported functions in Table API and SQL.
-* [Connect to External Systems]({% link dev/table/connect.md %}): Available connectors and formats for reading and writing data to external systems.
+* [SQL]({% link dev/table/sql/index.zh.md %}): Supported operations and syntax for SQL.
+* [SQL Client]({% link dev/table/sqlClient.zh.md %}): Play around with Flink SQL and submit a table program to a cluster without programming knowledge
+* [Concepts & Common API]({% link dev/table/common.zh.md %}): Shared concepts and APIs of the Table API and SQL.
+* [Streaming Concepts]({% link dev/table/streaming/index.zh.md %}): Streaming-specific documentation for the Table API or SQL such as configuration of time attributes and handling of updating results.
+* [Built-in Functions]({% link dev/table/functions/systemFunctions.zh.md %}): Supported functions in Table API and SQL.
+* [Connect to External Systems]({% link dev/table/connect.zh.md %}): Available connectors and formats for reading and writing data to external systems.
 
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