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 (
    86429, 86430, 86431, 86432, 86440, 86441, 
    86439, 86442, 86433, 86438, 86434, 
    86437, 86435, 86436, 86449, 86448, 
    86447, 86446, 86445, 86444, 86453, 
    86452, 86443, 86451, 86450, 86457, 
    86456, 86455, 86454, 86631, 86632
  )

Query time 0.00125

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": 31,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (86429,86430,86431,86432,86440,86441,86439,86442,86433,86438,86434,86437,86435,86436,86449,86448,86447,86446,86445,86444,86453,86452,86443,86451,86450,86457,86456,86455,86454,86631,86632)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}