SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    12363, 12349, 12351, 12350, 12353, 12352, 
    12355, 12354, 12362, 12360, 12361, 
    12358, 12359, 12356, 12357
  ) 
  AND feature_id IN (553, 625, 628, 627, 624) 
  AND lang_code = 'en'

Query time 0.00308

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "6.21"
    },
    "table": {
      "table_name": "cscart_product_features_values",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "fl",
        "lang_code",
        "product_id",
        "fpl",
        "idx_product_feature_variant_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "key_length": "15",
      "rows_examined_per_scan": 14,
      "rows_produced_per_join": 14,
      "filtered": "100.00",
      "using_index_for_skip_scan": true,
      "cost_info": {
        "read_cost": "4.81",
        "eval_cost": "1.40",
        "prefix_cost": "6.21",
        "data_read_per_join": "10K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`test2_gaseus`.`cscart_product_features_values`.`product_id` in (12363,12349,12351,12350,12353,12352,12355,12354,12362,12360,12361,12358,12359,12356,12357)) and (`test2_gaseus`.`cscart_product_features_values`.`feature_id` in (553,625,628,627,624)) and (`test2_gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id feature_id variant_id
12349 553 1935
12350 553 1935
12351 553 1935
12352 553 1935
12353 553 1935
12354 553 1935
12355 553 1935
12356 553 1935
12357 553 1935
12358 553 1935
12359 553 1935
12360 553 1935
12361 553 1935
12362 553 1935
12363 553 1935
12349 624 2403
12350 624 2403
12351 624 2403
12352 624 2403
12353 624 2403
12354 624 2403
12355 624 2403
12356 624 2403
12357 624 2403
12358 624 2403
12359 624 2403
12360 624 2403
12361 624 2403
12362 624 2403
12363 624 2403
12349 625 2133
12350 625 2134
12351 625 2135
12352 625 2136
12353 625 2388
12354 625 2133
12355 625 2134
12356 625 2135
12357 625 2136
12358 625 2388
12359 625 2133
12360 625 2134
12361 625 2135
12362 625 2136
12363 625 2388
12349 627 2378
12350 627 2378
12351 627 2378
12352 627 2378
12353 627 2378
12354 627 1836
12355 627 1836
12356 627 1836
12357 627 1836
12358 627 1836
12359 627 1954
12360 627 1954
12361 627 1954
12362 627 1954
12363 627 1954
12349 628 1660
12350 628 1660
12351 628 1660
12352 628 1660
12353 628 1660
12354 628 1660
12355 628 1660
12356 628 1660
12357 628 1660
12358 628 1660
12359 628 1660
12360 628 1660
12361 628 1660
12362 628 1660
12363 628 1660