When talking about lakes in Scotland,people generally use the Gaelic word for lake 'loch',but pronounce it

I dunno about Wales but in Ireland we pronounce it the same as the scots. You are right that English people are just not used to this sound "ch" which doesn't exist in the english language. It is like how it is difficult for us to pronounce the french "r" etc.... We haven't been brought up with these sounds so we can't emulate them.