SELECT 
  cscart_product_feature_variant_descriptions.*, 
  cscart_product_feature_variants.* 
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 = 'ja' 
WHERE 
  1 
  AND cscart_product_feature_variants.feature_id IN (18) 
ORDER BY 
  cscart_product_feature_variants.position, 
  cscart_product_feature_variant_descriptions.variant 
LIMIT 
  0, 14

Query time 0.00007

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_product_feature_variants.position, cscart_product_feature_variant_descriptions.variant",
      "temporary_table": {
        "table": {
          "table_name": "cscart_product_feature_variants",
          "access_type": "range",
          "possible_keys": ["feature_id"],
          "key": "feature_id",
          "key_length": "3",
          "used_key_parts": ["feature_id"],
          "rows": 53,
          "filtered": 100,
          "index_condition": "cscart_product_feature_variants.feature_id = 18"
        },
        "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": [
            "smscrm_edev.cscart_product_feature_variants.variant_id",
            "const"
          ],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "trigcond(cscart_product_feature_variant_descriptions.lang_code = 'ja')"
        }
      }
    }
  }
}