SELECT 
  cscart_product_feature_variant_descriptions.*, 
  cscart_product_feature_variants.*, 
  cscart_seo_names.name as seo_name, 
  cscart_seo_names.path as seo_path 
FROM 
  cscart_product_feature_variants 
  LEFT JOIN cscart_product_feature_variant_descriptions ON cscart_product_feature_variant_descriptions.variant_id = cscart_product_feature_variants.variant_id 
  AND cscart_product_feature_variant_descriptions.lang_code = 'es' 
  LEFT JOIN cscart_seo_names ON cscart_seo_names.object_id = cscart_product_feature_variants.variant_id 
  AND cscart_seo_names.type = 'e' 
  AND cscart_seo_names.dispatch = '' 
  AND cscart_seo_names.lang_code = 'es' 
WHERE 
  1 
  AND cscart_product_feature_variants.feature_id IN (639) 
ORDER BY 
  cscart_product_feature_variants.position, 
  cscart_product_feature_variant_descriptions.variant

Query time 0.00222

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_product_feature_variants.position, cscart_product_feature_variant_descriptions.variant",
      "temporary_table": {
        "nested_loop": [
          {
            "table": {
              "table_name": "cscart_product_feature_variants",
              "access_type": "ref",
              "possible_keys": ["feature_id"],
              "key": "feature_id",
              "key_length": "3",
              "used_key_parts": ["feature_id"],
              "ref": ["const"],
              "rows": 2,
              "filtered": 100
            }
          },
          {
            "table": {
              "table_name": "cscart_product_feature_variant_descriptions",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "9",
              "used_key_parts": ["variant_id", "lang_code"],
              "ref": [
                "live_clonned.cscart_product_feature_variants.variant_id",
                "const"
              ],
              "rows": 1,
              "filtered": 100,
              "attached_condition": "trigcond(cscart_product_feature_variant_descriptions.lang_code = 'es')"
            }
          },
          {
            "table": {
              "table_name": "cscart_seo_names",
              "access_type": "ref",
              "possible_keys": ["PRIMARY", "dispatch"],
              "key": "PRIMARY",
              "key_length": "206",
              "used_key_parts": ["object_id", "type", "dispatch", "lang_code"],
              "ref": [
                "live_clonned.cscart_product_feature_variants.variant_id",
                "const",
                "const",
                "const"
              ],
              "rows": 2,
              "filtered": 100,
              "attached_condition": "trigcond(cscart_seo_names.`type` = 'e' and cscart_seo_names.dispatch = '' and cscart_seo_names.lang_code = 'es')"
            }
          }
        ]
      }
    }
  }
}