This is an example of a migration to move translated messages from Yii php files to lajax yii2-translate

sample_migration.php

<?php

use lajax\translatemanager\models\LanguageSource;
use lajax\translatemanager\models\LanguageTranslate;
use yii\db\Migration;

/**
 * Class m190402_151021_move_translations_to_db
 */
class m190402_151021_move_translations_to_db extends Migration
{

    protected $tempTableName = 'gvp_translate';

    /**
     * {@inheritdoc}
     */
    public function safeUp()
    {
        $this->delete(LanguageTranslate::tableName(), ['language' => 'es-ES']);

        $files = glob(Yii::getAlias('@app/messages') . '/??/*.php');

        foreach ($files as $file) {
            $messages = include($file);
            $category = pathinfo($file, PATHINFO_BASENAME);

            $this->createTempTable();

            $messages = array_filter($messages, function ($val) {
                return !empty($val);
            });


            array_walk($messages, function (&$value, $key) use ($category) {
                $value = ['es-ES', $value, $key];
            });
            $this->batchInsert($this->tempTableName, [
                'language',
                'translation',
                'message'
            ], $messages);

            $translationsTableName = LanguageTranslate::tableName();
            $sourceTableName = LanguageSource::tableName();

            $sql2 = <<<MYSQL
            INSERT INTO {$translationsTableName} (SELECT a.id,t.language,t.translation FROM {$this->tempTableName} AS t INNER JOIN {$sourceTableName} a ON BINARY a.message= t.message)
MYSQL;

            $this->execute($sql2);
            $this->dropTable($this->tempTableName);
        }
    }


    public function createTempTable()
    {

        $sql = <<<MYSQL

create temporary table {$this->tempTableName}
(
  id          int        not null,
  language    varchar(5) not null,
  translation text       null,
  message text       null
)
MYSQL;

        $this->execute($sql);
    }

    /**
     * {@inheritdoc}
     */
    public function safeDown()
    {
        return true;
    }

    /*
    // Use up()/down() to run migration code without a transaction.
    public function up()
    {

    }

    public function down()
    {
        echo "m190402_151021_move_translations_to_db cannot be reverted.\n";

        return false;
    }
    */
}