These sticks are sold on eBay for as little as 250 Baht / 5 Euros.

The stick's software is in this case German. How would you go about this?

1.) Replace the stick's software with the Thai version?

2.) Forget it and buy a local stick?

Modern mobile phones work well when used as modem to connect to the internet. But I prefer such a stick to a cell phone.

Any comments?

Check and make sure that they offer at minimum EDGE. UMTS is not deployed in Thailand and if you bring a usb modem and it does not have EDGE also it will default to GPRS....not a good speed. Granted, if they are HSDPA and you live in an area that has coverage and it's the same frequency that is a plus. 5 (five) Euros is pocket change so go ahead and do it.

As far as software; unless you're going to use a connection monitor you can use the built in dial-up feature in your Operating System and just install the drivers to make the modem work.