I did try flying a glider in cloud once only! And announced my intention on the cloud flying glider frequency as required, sure enough there was another glider in the cloud, and we told each other how high in the cloud, so all well.
EXCEPT I had CFE (field elevation) instead of AMSL (sea level) set on the alt! so my proper calls may have been quite incorrect! so this old woman chickened out from flying gliders in cloud, and most glider pilots who do so are fully qualified commercial pilots of vast experience, and I believe in Europe this is not permitted anyhow, only in the UK. Most glider pilots would not get worried by occasional penetration on the underside of a nice cu, but these days I don't even like to do that, keeping enough space under the cloud to be able to spot cross country gliders dolphining toward me...
Got the IR in Texas but don't use that any more either.....