MigrateSQLMap for subfields

The issue is that you need the language in addition to the ID to uniquely identify items, correct? You can add additional columns to the keys in MigrateSQLMap:

    $this->map = new MigrateSQLMap($this->machineName,
        array(
          'style' => array('type' => 'varchar',
                           'length' => 255,
                           'not null' => TRUE,
                           'description' => 'Topic ID',
                          ),
          'style_language' => array('type' => 'varchar',
                           'length' => 3,
                           'not null' => TRUE,
                           'description' => 'Language of the style',
                          ),
        ),
        MigrateDestinationTerm::getKeySchema()
      );

This will give you both sourceid1 and sourceid2 in the map table.

When providing more info to an issue marked "Postponed (maintainer needs more info)", be sure to set the status back to Active for more visibility.

In my example, above, 'style' and 'style_language' represent columns from your source data. So, if your CSV file looks something like:

style,style_language
School,en
Ecole,fr

then the map table would be populated like

where the destid1 values are the Drupal term IDs created for each term.