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 (
    70707, 70706, 70705, 70704, 70708, 70722, 
    70721, 70720, 70719, 70718, 70723, 
    70728, 70727, 70726, 70725, 70724, 
    70729, 70733, 70732, 70731, 70730, 
    70734, 70738, 70737, 70736, 70735, 
    70739, 70743, 70742, 70741, 70740, 
    70744
  )

Query time 0.00139

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": 32,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (70707,70706,70705,70704,70708,70722,70721,70720,70719,70718,70723,70728,70727,70726,70725,70724,70729,70733,70732,70731,70730,70734,70738,70737,70736,70735,70739,70743,70742,70741,70740,70744)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}