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 = 'en' 
WHERE 
  pfv.variant_id IN (
    70887, 70886, 70888, 70892, 70891, 70890, 
    70889, 70893, 70895, 70894, 70896, 
    70898, 70897, 70899, 70905, 70904, 
    70903, 70906, 83821, 83822, 83823, 
    83824, 83825
  )

Query time 0.00987

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": 23,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (70887,70886,70888,70892,70891,70890,70889,70893,70895,70894,70896,70898,70897,70899,70905,70904,70903,70906,83821,83822,83823,83824,83825)"
        }
      },
      {
        "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 = 'en'"
        }
      }
    ]
  }
}