Does Framemaker support these languages Khmer, Burmese and Sinhala?

> In the former situation, probably yes if you’ve got the fonts for those languages ...

Assuming we're speaking of Unicode, those South Asian scripts are overflowing with non-advancing diacritics, many of which may be used in multiple combinations. Not having done more than minimal testing of support for arbitrary NADs in FM, I wouldn't assume it works even if the font code points are populated. (I'm perfectly willing to be mistaken, of course.)

And then there are the usual novel-language issues of spell-checking, hyphenation (assuming the script supports it), FM support for possibly important invisible operators and right-to-left (if required, typically not with these languages).

Unicode - it's not just characters anymore. The Consortium managed to avoid Shift-In/Shift-Out/Escapes (other than to preserve the legacy ASCII for those control characters), but brought in an army of code points for layout control, variation selector, and characters with implicit formatting. Just browsing the Code Charts, I'm personally glad I don't have to write code to render any of it, and I suspect few apps correctly render more than a fraction of it, whether the instant font is populated for the desired script or not.