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 (
    53, 2, 14, 217, 12, 124, 135, 4, 16, 27, 
    215, 218, 143, 292, 465, 293, 343, 374, 
    33, 426, 499, 595, 521, 626, 654, 708, 
    722, 720, 724, 729, 833, 875, 390, 924, 
    945, 163, 1009, 164
  ) 
ORDER BY 
  cscart_product_feature_variants.position ASC, 
  udf_NaturalSortFormat(
    cscart_product_feature_variant_descriptions.variant, 
    10, "."
  ) ASC

Query time 0.00256

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "39.91"
    },
    "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": 38,
            "rows_produced_per_join": 38,
            "filtered": "100.00",
            "index_condition": "(`dbggbern`.`cscart_product_feature_variants`.`variant_id` in (53,2,14,217,12,124,135,4,16,27,215,218,143,292,465,293,343,374,33,426,499,595,521,626,654,708,722,720,724,729,833,875,390,924,945,163,1009,164))",
            "cost_info": {
              "read_cost": "22.81",
              "eval_cost": "3.80",
              "prefix_cost": "26.61",
              "data_read_per_join": "43K"
            },
            "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": 38,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "9.50",
              "eval_cost": "3.80",
              "prefix_cost": "39.91",
              "data_read_per_join": "114K"
            },
            "used_columns": [
              "variant_id",
              "variant",
              "lang_code"
            ]
          }
        }
      ]
    }
  }
}