The shardCollection command should have the following collation-related behavior:

• It should optionally accept a collation parameter. If supplied, the parameter must currently have the value {locale: "simple"}, since non-simple collations are not permitted on the shard key.
• If the collection being sharded has a non-simple default collation, then the command will fail unless {locale: "simple"} is explicitly supplied by the application.
• If the collection already exists and is non-empty, an index whose prefix is the shard key must be present, and must have the simple collation.