multilingual text image generation

Could someone help with this:
I am trying to auto-generate images from multilingual text passed to the GD
library image functions.
I am using some Thai text to create images and I don't get the proper image,
which appears to be a charset problem, but I can't be sure. 
While using the utf8_decode or html_entity_decode functions on the following
string (encoded html)
"สวัสดีค่ะ"

I see the Thai characters on the rendered html page, but I get other
characters when using utf-8 for the string passed for image generation using
the functions: imagettftext() and imagepng().

The HTML content meta tag is specified as charset=utf-8.
My PHP installation includes mbstring and iconv support.
mbstring.http_output and mbstring.internal_encoding is set to UTF-8
and mbstring.language set to Neutral [which should default to UTF-8 too]

Can I use UTF-8 for Thai characters or would I need to set charset to
tis620_bin

There is also the possibility of using other languages.

Naintara

-- 
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.371 / Virus Database: 267.14.18/230 - Release Date: 14-Jan-06