The Thai language is supported by code page TIS 620-2533. This is a single-byte code page for which some of the codepoints are combining characters. A single column could consist of up to three 620-2533 codepoints; however, it is not a multi-byte code page consisting of lead-byte and trail-byte combinations.
There are two files for Thai collation:
OpenEdge/prolang/tai/thai-old.df — Contains the "THAI" collation for codepage TIS 620-2533. This collation assigns a single weight to each character for case-sensitive and case-insensitive sorting. Although adequate for many applications, this collation does not follow Thai conventions for prefix vowels or treatment of strings as collation units of multiple characters. This collation was provided in Progress versions prior to 9.1A and 8.3C, and is still provided for backward compatibility.
OpenEdge/prolang/tai/thai.df — Contains the "BASIC" collation for TIS 620-2533. This collation takes prefix vowels into account when sorting. It also treats strings as containing collation units of multiple characters.
To check for further information on Thai code page issues, you can find the following readme file in your OpenEdge installation if you specified Thai language support during the install process: OpenEdge\prolang\tai\readme.
OpenEdge/prolang/tai/thai-old.df — Contains the "THAI" collation for codepage TIS 620-2533. This collation assigns a single weight to each character for case-sensitive and case-insensitive sorting. Although adequate for many applications, this collation does not follow Thai conventions for prefix vowels or treatment of strings as collation units of multiple characters. This collation was provided in Progress versions prior to 9.1A and 8.3C, and is still provided for backward compatibility.