Originally Posted by
goma
Thanks Goldorak. Yes I'm Vietnamese. I actually emailed the Embassy of France in Vietnam asking about the requirements 3 days ago but they haven't replied me yet... (and they refused to answer questions on visa via phone

)
Be sure, when you enquire, that you precise that you will actually enter France because you will clear immigration. This is potentially completely different from a classical international transit when you're staying in the int'l transit zone and not entering the country you are transiting in.
Originally Posted by
goma
My flights are from the same terminal, so I assume I won't have to go through security check many times? (I read somewhere that going to different terminal requires security check 5-6 times or so). This is my 1st time at CDG so I'm a bit worried.
Certainly not 5 or 6 times

you will arrive in 2E, clear French immigration, collect your bags, clear customs (although you may not notice it unless you a stopped for a search). Then you arrive in the public zone (arrival area). You'll have to go one floor up (departure level), check-in to GLA (note that BE handled by AF in CDG), re-clear French immigration (you leave the Schengen area), pass security and finally take your flight

Of course you will have to clear UK Immgration arriving in GLA.