Does the hydrocele is seriuos disease. And is there treatement rather than surgery?

No and yes. A hydrocele is not a serious condition by itself. However, it should be evaluated to ensure that the cause of the hydrocele is not something serious (ie it is a more of a symptom than a disease). Surgery will cure most. Observation is prudent if there are no symptoms. From time to time a physician may elect to aspirate the hydrocele.
Not often worrisome. A hydrocele is a collection of fluid around the testicle. Often the reason for this is unclear, but infection, trauma, tumors, or other causes are possible, so medical evaluation is important. It requires treatment when large enough to preclude palpating of the testicle or so large as to be uncomfortable. Drainage without surgery rarely works as the fluid recollects. The operation is outpatient.
Not serious. A hydrocele is a collection of fluid around the testicle which causes a sometimes bothersome swelling in the scrotum. For large, symptomatic hydroceles, surgical removal is the only treatment. For small, not bothersome hydroceles, observation could be considered. Be sure to have an exam by your physician to rule out other, more serious causes of scrotal/testicle swelling.