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 = 'vi' 
WHERE 
  pfv.variant_id IN (
    68327, 68328, 68336, 68335, 68334, 68333, 
    68332, 68337, 68347, 68346, 68345, 
    68344, 68343, 68348, 68352, 68351, 
    68350, 68349, 68353, 71520, 71519, 
    71518, 71521, 73307, 73306, 73527, 
    73526, 74986, 74985, 74984, 74983, 
    74987, 76698, 76697, 76741, 76740, 
    76742, 76888, 76886, 76887, 77936, 
    77934, 77935, 77945, 77943, 77944, 
    78278, 78277, 78426, 78651, 79232, 
    79233, 79234, 79244, 79242, 79243, 
    79632, 79633, 79634, 79635, 79644, 
    79645, 74407, 82455, 74412, 82456, 
    84336, 84335
  )

Query time 0.00316

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["variant_id"],
          "rows": 68,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (68327,68328,68336,68335,68334,68333,68332,68337,68347,68346,68345,68344,68343,68348,68352,68351,68350,68349,68353,71520,71519,71518,71521,73307,73306,73527,73526,74986,74985,74984,74983,74987,76698,76697,76741,76740,76742,76888,76886,76887,77936,77934,77935,77945,77943,77944,78278,78277,78426,78651,79232,79233,79234,79244,79242,79243,79632,79633,79634,79635,79644,79645,74407,82455,74412,82456,84336,84335)"
        }
      },
      {
        "table": {
          "table_name": "pfvd",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "ref": ["dev_db.pfv.variant_id", "const"],
          "rows": 1,
          "filtered": 100,
          "index_condition": "pfvd.lang_code = 'vi'"
        }
      }
    ]
  }
}