SELECT 
  pfv.variant_id, 
  pfv.position, 
  pfvd.variant 
FROM 
  cscart_product_feature_variants AS pfv 
  INNER JOIN cscart_product_feature_variant_descriptions AS pfvd ON pfv.variant_id = pfvd.variant_id 
  AND pfvd.lang_code = 'ru' 
WHERE 
  pfv.variant_id IN (
    6, 1362, 1361, 1360, 1359, 1358, 1357, 
    1370, 1369, 1368, 1367, 1366, 1365, 
    1371, 1373, 1392, 1391, 1390
  )

Query time 0.00066

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "18.91"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "rows_examined_per_scan": 18,
          "rows_produced_per_join": 18,
          "filtered": "100.00",
          "index_condition": "(`test_uchur_k`.`pfv`.`variant_id` in (6,1362,1361,1360,1359,1358,1357,1370,1369,1368,1367,1366,1365,1371,1373,1392,1391,1390))",
          "cost_info": {
            "read_cost": "10.81",
            "eval_cost": "1.80",
            "prefix_cost": "12.61",
            "data_read_per_join": "27K"
          },
          "used_columns": [
            "variant_id",
            "position"
          ]
        }
      },
      {
        "table": {
          "table_name": "pfvd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "test_uchur_k.pfv.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 18,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "4.50",
            "eval_cost": "1.80",
            "prefix_cost": "18.91",
            "data_read_per_join": "56K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}