Toggles translatability of the given field.
This is called from a batch operation, but should only run once per field.
bool $translatable: Indicator of whether the field should be made translatable (TRUE) or untranslatble (FALSE).
string $field_name: Field machine name.
function translation_entity_translatable_switch($translatable, $field_name) {
$field = field_info_field($field_name);
if ($field['translatable'] === $translatable) {
return;
}
$field['translatable'] = $translatable;
field_update_field($field);
}