Pango version 1.8 was released in December of 2004. In this chart, stars indicate full OpenType support for scripts in Pango version 1.8.
Eric Mader, the author of ICU's Layout Engine, ported OpenType support for the majority of Indic scripts to Pango about two years ago.
The Arabic support includes full OpenType support for vowel marks and positioning for Nashtaliq slanted baselines needed for languages like Urdu. Hebrew support includes OpenType support to position cantillation marks.
Release 1.8 added support for Syriac, Sinhala, Lao, and Tibetan scripts. The KhmerOS project1 is working on Khmer support in Pango. As of this writing (Feb. '05) the Khmer module was in the process of being reviewed and revised prior to incorporation into the next release of Pango. The next release of Pango is scheduled for mid-2005, so it is likely that Khmer support will be included in Pango 1.10. Thaana is an RTL script, but is not cursive. Since Pango has OpenType support for Hebrew, it is possible that Thaana may work in Pango but I have not been able to confirm this.
1. KhmerOS is a project to bring Khmer to computers, http://www.khmeros.info.