init.php

<?php

$connection->registerFilter('translate', array($translator, 'translate'), Connection::WIRE_ENTITY | Connection::WIRE_PROPERTY);
$connection->registerFilter('translateByTable', array($translator, 'translateByTable'));

Mapper.php

<?php

namespace Model;

class Mapper extends \LeanMapper\DefaultMapper implements ITranslatingMapper
{

  	/**
	 * @return string
	 */
	public function getLangTable()
	{
		return 'lang';
	}

	/**
	 * @param string $table
	 * @return string
	 */
	public function getTranslationTable($table)
	{
		return $table . '_translation';
	}
	
}

TranslatableEntity.php

<?php

namespace Model\Entity;

/**
 * @property Lang $lang m:hasOne m:translatable
 */
abstract class TranslatableEntity extends \LeanMapper\Entity
{

	/**
	 * @return array
	 */
	public function getTranslatableColumns()
	{
		$columns = array();
		foreach ($this->getCurrentReflection()->getEntityProperties() as $property) {
			if ($property->hasCustomFlag('translatable')) {
				$columns[] = $property->getColumn();
			}
		}
		return $columns;
	}

}

TranslatingRepository.php

<?php

namespace Model\Repository;

use Exception;
use LeanMapper\Connection;
use LeanMapper\Entity;
use LeanMapper\Events;
use Model\Entity\Lang;
use Model\Entity\TranslatableEntity;
use Model\ITranslatingMapper;

abstract class TranslatingRepository extends \LeanMapper\Repository
{

	/** @var LangRepository */
	private $langRepository;


	/**
	 * @param Connection $connection
	 * @param ITranslatingMapper $mapper
	 * @param LangRepository $langRepository
	 */
	public function __construct(Connection $connection, ITranslatingMapper $mapper, LangRepository $langRepository)
	{
		parent::__construct($connection, $mapper);
		$this->langRepository = $langRepository;
	}

	/**
	 * @param mixed $id
	 * @param Lang $lang
	 * @return Entity
	 * @throws Exception
	 */
	public function find($id, Lang $lang)
	{
		$table = $this->getTable();
		$row = $this->connection->select('%n.*', $table)
				->from($table)
				->where('%n.%n = %i', $table, $this->mapper->getPrimaryKey($table), $id)
				->applyFilter('translateByTable', $table, $lang)
				->fetch();

		if ($row === false) {
			throw new Exception('Entity was not found.');
		}
		return $this->createEntity($row);
	}

	/**
	 * @param Lang $lang
	 * @return Entity[]
	 */
	public function findAll(Lang $lang)
	{
		$table = $this->getTable();
		return $this->createEntities(
			$this->connection->select('%n.*', $table)
					->from($table)
					->applyFilter('translateByTable', $table, $lang)
					->fetchAll()
		);
	}

	/**
	 * @param Entity $entity
	 * @return mixed
	 */
	protected function insertIntoDatabase(Entity $entity)
	{
		$table = $this->getTable();

		$mapper = $this->mapper;
		$primaryKey = $mapper->getPrimaryKey($table);
		$translationTable = $mapper->getTranslationTable($table);
		$relationshipColumn = $mapper->getRelationshipColumn($translationTable, $table);
		$langRelationshipColumn = $mapper->getRelationshipColumn($translationTable, $mapper->getLangTable());

		list($primaryValues, $translatedValues) = $this->getSeparatedModifierRowData($entity);

		$this->connection->query(
			'INSERT INTO %n %v', $table, $primaryValues
		);
		$id = isset($primaryValues[$primaryKey]) ? $primaryValues[$primaryKey] : $this->connection->getInsertId();

		$translatedValues[$relationshipColumn] = $id;

		foreach ($this->langRepository->findAll() as $lang) {
			$values = $translatedValues;
			if ($translatedValues[$langRelationshipColumn] !== $lang->id) {
				$values = array(
					$relationshipColumn => $id,
					$langRelationshipColumn => $lang->id
				);
			}
			$this->connection->query(
				'INSERT INTO %n %v', $translationTable, $values
			);
		}
		return $id;
	}

	/**
	 * @param Entity $entity
	 * @return mixed
	 */
	protected function updateInDatabase(Entity $entity)
	{
		$table = $this->getTable();

		$mapper = $this->mapper;
		$primaryKey = $mapper->getPrimaryKey($table);
		$idField = $mapper->getEntityField($table, $primaryKey);
		$translationTable = $mapper->getTranslationTable($table);
		$relationshipColumn = $mapper->getRelationshipColumn($translationTable, $table);
		$langRelationshipColumn = $mapper->getRelationshipColumn($translationTable, $mapper->getLangTable());

		list($primaryValues, $translatedValues) = $this->getSeparatedModifierRowData($entity);

		if (!empty($primaryValues)) {
			$this->connection->query(
				'UPDATE %n SET %a WHERE %n = ?', $table, $primaryValues, $primaryKey, $entity->$idField
			);
		}
		if (!empty($translatedValues)) {
			$this->connection->query(
				'UPDATE %n SET %a', $translationTable, $translatedValues,
				'WHERE %n = %i AND %n = %s', $relationshipColumn, $entity->$idField, $langRelationshipColumn, $entity->lang->id
			);
		}
	}

	////////////////////
	////////////////////

	/**
	 * @param TranslatableEntity $entity
	 * @return array
	 */
	private function getSeparatedModifierRowData(TranslatableEntity $entity)
	{
		$translatableColumns = array_flip($entity->getTranslatableColumns());
		$primaryValues = array();
		$translatedValues = array();
		foreach ($entity->getModifiedRowData() as $column => $value) {
			if (isset($translatableColumns[$column])) {
				$translatedValues[$column] = $value;
			} else {
				$primaryValues[$column] = $value;
			}
		}
		return array($primaryValues, $translatedValues);
	}

}

Translator.php

<?php

namespace Model\Filter;

use LeanMapper\Fluent;
use LeanMapper\Reflection\Property;
use Model\Entity\Lang;
use Model\Entity\TranslatableEntity;
use Model\ITranslatingMapper;

class Translator
{

	/** @var ITranslatingMapper */
	private $mapper;


	/**
	 * @param ITranslatingMapper $mapper
	 */
	public function __construct(ITranslatingMapper $mapper)
	{
		$this->mapper = $mapper;
	}

	/**
	 * @param Fluent $statement
	 * @param TranslatableEntity $entity
	 * @param Property $property
	 * @param Lang $lang
	 */
	public function translate(Fluent $statement, TranslatableEntity $entity, Property $property, Lang $lang = null)
	{
		if ($lang === null) {
			$lang = $entity->lang;
		}
		$targetTable = $property->getRelationship()->getTargetTable();
		$this->translateByTable($statement, $targetTable, $lang);
	}

	/**
	 * @param Fluent $statement
	 * @param string $targetTable
	 * @param Lang $lang
	 */
	public function translateByTable(Fluent $statement, $targetTable, Lang $lang)
	{
		$translationTable = $this->mapper->getTranslationTable($targetTable);
		$statement->removeclause('select')
				->select('%n.*, %n.*', $translationTable, $targetTable)
				->leftJoin('%n', $translationTable)->on(
					'%n.%n = %n.%n',
					$translationTable,
					$this->mapper->getRelationshipColumn($translationTable, $targetTable),
					$targetTable,
					$this->mapper->getPrimaryKey($targetTable)
				)
				->where('%n = %s', $this->mapper->getRelationshipColumn($translationTable, $this->mapper->getLangTable()), $lang->id);
	}

}