SELECT 
  b.variant_name, 
  a.* 
FROM 
  cscart_product_option_variants AS a 
  LEFT JOIN cscart_product_option_variants_descriptions AS b ON b.variant_id = a.variant_id 
  AND b.lang_code = 'de' 
WHERE 
  1 
  AND a.option_id IN (4, 21) 
  AND a.status = 'A' 
ORDER BY 
  a.position, 
  a.variant_id

Query time 0.00032

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.050240031,
    "nested_loop": [
      {
        "read_sorted_file": {
          "filesort": {
            "sort_key": "a.position, a.variant_id",
            "table": {
              "table_name": "a",
              "access_type": "range",
              "possible_keys": ["status", "option_id", "option_id_2"],
              "key": "option_id",
              "key_length": "6",
              "used_key_parts": ["option_id", "status"],
              "loops": 1,
              "rows": 16,
              "cost": 0.0216164,
              "filtered": 100,
              "index_condition": "a.option_id in (4,21) and a.`status` = 'A'"
            }
          }
        }
      },
      {
        "table": {
          "table_name": "b",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "ref": ["u428615623_ecartifygonje.a.variant_id", "const"],
          "loops": 16,
          "rows": 1,
          "cost": 0.01840704,
          "filtered": 100,
          "attached_condition": "trigcond(b.lang_code = 'de')"
        }
      }
    ]
  }
}