This is used for multilingual table data (see the shipped Title table for an example of a multilingual table).
If multilingual table data is not required, set this to the value "No Language Field - Monolingual Table Data"
A table does not necessarily have to be multilingual just because the partition is multilingual. But if multilingual data is required, use this parameter to specify which table field will contain the language code for a table row. A language field must also be a key field.
This property is in the Code Table Definition tab.