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 (
    78091, 78090, 78116, 78117, 78118, 78119, 
    78120, 78121, 78122, 78123, 78124, 
    78125, 78095, 78105, 78094, 78104, 
    78112, 78111, 78110, 78109, 78108, 
    78107, 78106, 78096, 78097, 78098, 
    78099, 78100, 78101, 78102, 78103
  )

Query time 0.00314

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 (78091,78090,78116,78117,78118,78119,78120,78121,78122,78123,78124,78125,78095,78105,78094,78104,78112,78111,78110,78109,78108,78107,78106,78096,78097,78098,78099,78100,78101,78102,78103)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}