"Dydd Llun, Dydd Mawrth"
It seems some speakers do say it like the 'ch' in German 'ich' (although the Welsh 'ch' is never that way - only like in German 'bach'). At the same time, it's not considered 'proper', and the 'proper' way (as far as there is such a thing) is not that difficult to learn if you have good resources.
The linguist who manages this blog noticed the 'ich' pronunciation on a BBC webpage and asked the Welsh Commission (heavily staffed by native speakers) about it - apparently they saw nothing out of the ordinary about it.
Just scroll down to Thursday 26 June 2008 and Tuesday 17 June 2008 (don't worry, it's the archive for June 2008, so it's not that far down!): http://www.phon.ucl.ac.uk/home/wells/blog0806b.htm
I think Gwybodiadur has a good approach to ll (and to Welsh in general): http://gwybodiadur.co.uk/