Perdre ses billes? Means aboslutely nothing in French, lol. I just love those colloquial expressions which just cannot be translated without totally losing the meaning. I got caught out once, not with the words, which I had translated correctly- but with the accompanying gesture, I had not!! In English you say 'my foot' when you don't believe somebody (or pull the other one)- but in French we say 'mon oeil' (my eye) and point to said eye. One day a kid at school told me he hadn't done his homework because his dog had been run over- but I knew from his expression (and past history) that he was pulling my leg- so I said 'my foot' but automatically pointed to my eye. He asked why I did that- 'Did what' I replied. It was really funny as I had no idea I was regularly doing this!!!
German had a big simplification review not that long ago- but I've not heard of getting rid of der, die, das- because of the declension system (for instance, der, becomes, den- when it is the direct object, and dem, when it is the indirect object, etc, etc)- it would mean not just replacing der, die, das- but all the declension system- which would be huge and destroy the language imho, and sad.