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 (
    71601, 71600, 71599, 71598, 71602, 71610, 
    71609, 71608, 71607, 71606, 71605, 
    71604, 71603, 71611, 71616, 71614, 
    71613, 71612, 71615, 71621, 71619, 
    71618, 71617, 71620, 71626, 71624, 
    71623, 71622, 71625, 71631, 71629, 
    71628, 71627, 71630
  )

Query time 0.00214

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": 34,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (71601,71600,71599,71598,71602,71610,71609,71608,71607,71606,71605,71604,71603,71611,71616,71614,71613,71612,71615,71621,71619,71618,71617,71620,71626,71624,71623,71622,71625,71631,71629,71628,71627,71630)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}