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 (
    68677, 68676, 68680, 68679, 68778, 68777, 
    75974, 75969, 75970, 75971, 75972, 
    75973, 78672, 78673, 79019, 79018, 
    79251, 79252, 80381, 84477, 84479, 
    86637, 86638, 86882, 86883
  )

Query time 0.00297

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 (68677,68676,68680,68679,68778,68777,75974,75969,75970,75971,75972,75973,78672,78673,79019,79018,79251,79252,80381,84477,84479,86637,86638,86882,86883)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}