I just finished rooting my Nexus One and installed Thai fonts onto it. I had to use several websites to complete this task, but I wanted to collect them all into once nice place for any stumblers. The purpose of installing Thai fonts onto my Nexus One was to have the ability to read Thai on my Facebook app as well as some Thai websites.
Here’s how to do it:
Step 1: Root your phone. You can read about that and watch a video: Video: How to unlock and root a Nexus One.
Step 2: Watch the Thai video of how this guy did it. Thai font for Nexus One. I also downloaded the Thai fonts here (source: Droidsans.com). You can read and see pics of the steps too at: Android Review: แกะกล่อง Nexus One ฉบับย่อ พร้อม Root ลงไทย By PDAMobiz.