SELECT 
  cscart_product_feature_variants.variant_id, 
  cscart_product_feature_variants.position, 
  cscart_product_feature_variants.color, 
  cscart_product_feature_variant_descriptions.variant 
FROM 
  cscart_product_feature_variants 
  LEFT JOIN cscart_product_feature_variant_descriptions ON cscart_product_feature_variants.variant_id = cscart_product_feature_variant_descriptions.variant_id 
  AND cscart_product_feature_variant_descriptions.lang_code = 'de' 
WHERE 
  cscart_product_feature_variants.variant_id IN (
    3, 15, 17, 37, 379, 398, 411, 423, 296, 
    441, 309, 487, 16, 566, 22, 578, 594, 
    458, 606, 465, 29, 14, 676, 681, 705, 
    711, 639, 571, 769, 725, 0, 760, 818, 
    824, 823, 822, 881, 212, 155, 921, 904, 
    4, 185, 944, 906, 908
  ) 
ORDER BY 
  cscart_product_feature_variants.position ASC, 
  udf_NaturalSortFormat(
    cscart_product_feature_variant_descriptions.variant, 
    10, "."
  ) ASC

Query time 0.00182

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "48.31"
    },
    "ordering_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_product_feature_variants",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "variant_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 46,
            "rows_produced_per_join": 46,
            "filtered": "100.00",
            "index_condition": "(`dbggbern`.`cscart_product_feature_variants`.`variant_id` in (3,15,17,37,379,398,411,423,296,441,309,487,16,566,22,578,594,458,606,465,29,14,676,681,705,711,639,571,769,725,0,760,818,824,823,822,881,212,155,921,904,4,185,944,906,908))",
            "cost_info": {
              "read_cost": "27.61",
              "eval_cost": "4.60",
              "prefix_cost": "32.21",
              "data_read_per_join": "52K"
            },
            "used_columns": [
              "variant_id",
              "color",
              "position"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_product_feature_variant_descriptions",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "variant_id",
              "lang_code"
            ],
            "key_length": "9",
            "ref": [
              "dbggbern.cscart_product_feature_variants.variant_id",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 46,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "11.50",
              "eval_cost": "4.60",
              "prefix_cost": "48.31",
              "data_read_per_join": "139K"
            },
            "used_columns": [
              "variant_id",
              "variant",
              "lang_code"
            ]
          }
        }
      ]
    }
  }
}