Bangkok's main cycling store near Lumpini Park sells folders. Most everything bike-wise there is significantly more expensive than anywhere else due to a hefty import tax. Exceptions include Thai-made mountain bikes. You can get an Acera set up for about $200 US, but I would do that outside of Bangkok.

There is one store to avoid; Top Gear in Chiang Mai. Many have been ripped off by them, but some others say they are OK. At any rate, the other stores are cheaper and nicer.

Thai is no problem. I speak some (and some Mandarin), but most everyone speaks back to me in English. This is a country literally overrun with tourists. There are 10 million visitors per year. You will be lucky to really get to meet a Thai person unless you get off the beaten path!