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 (
    68396, 68397, 68399, 68398, 68400, 68829, 
    68830, 68831, 68832, 68833, 68834, 
    68835, 68839, 68838, 68837, 68836, 
    68840, 87234, 68841, 68877, 68876, 
    68875, 68874, 68873, 68872
  )

Query time 0.00565

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": 25,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (68396,68397,68399,68398,68400,68829,68830,68831,68832,68833,68834,68835,68839,68838,68837,68836,68840,87234,68841,68877,68876,68875,68874,68873,68872)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}