We haven't got any idioms in Leafoosish yet, but there is a saying: e'se bly fasil de ddir egyll ce dde sumeter se. It corresponds to the English "easier said than done", but the literal meaning is "it's easier to say needle than to submit [to one]". (I think you can guess what the reference is here -- what kind of needle do you "submit to"?)
And if you think that's dark and dreary on my part, you should see this thread
Please, if you will, forget that. It was my feeble attempt at being imaginative and not just parroting the Welsh saying "haws dweud mynydd na mynd drosto" (easier to say mountain than to go over it, for anyone who's missed the discussions where it came up).
Since then, I've come up with an idiom that's only used in the three languages of Cymrygath, a city in the south of Llyffw. It's pretty much always the same: aler tros
in Cymrygath Leafoosish (a dialect of my conlang), mynd dros
(mynt tros' in the local "pinyin") in Cymraeg y cathod, and aller troche
in the local French. It means literally "to go over", and it's a euphemism for "to steal". The fact that I came up with this is a sign that I've spent too much time thinking about the aforementioned mountain.