@Roberto ********
for people leaving in the Kingdom for more than 180 days in a solar year, any money transfer from abroad (remittance) is considered as an income as shall be declared. Whether to pay tax or not depends on many factors. If there is a DTA with your country and if tax have been already paid in the country of origin, which shall be demonstrated, you could not be requested to pay anything or to pay only the difference between the already paid wrt the tax to be paid in Thailand.
On this matter the situation is quite complicated.