I do not have a recent enough TeX to test it out unfortunately (and it
is not my top priority), but I would have expected you to ask to
somebody who knows vntex very well why such a thing is needed.
I'll contact Hàn Thế Thành,
His reply:
first, thanks for your effort to add vntex support to lyx.
lyx is cool and starting from version 1.5.* with unicode
support it is a really great tool for latex newbies. I tried
utf8 support with the 1.5.0RC* (and fired a bug
report :)
the problem you mentioned is caused by the fact that
vietnamese is not officially supported by babel, so
babel.sty doesn't contain (yet) a line saying
,--------
| \DeclareOption{vietnam}{\input{vietnam.ldf}}
`--------
I will send a mail to the babel maintainer then to ask him
to add this line.
regards Uwe
