Question: BIP39 specifies different word lists in different languages. But I wonder if the word list generated by a software that gives me French words (e.g. Copay on iOS) can be used to re-create the same wallet using another software that expects English words.

I looked at the section [From mnemonic to seed](https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki#From_mnemonic_to_seed) of the BIP39 specification. Given that the mnemonic sentence itself is fed through the [PBKDF2](https://en.wikipedia.org/wiki/PBKDF2) function, rather than first looking up the indices of the words in the dictionary, I guess that the answer is no, and a French list can't be easily converted into an English list. Is this correct?

Doesn't this drastically reduce the interoperability of wallets using different word lists? Specifically, how can I ensure that the word list I have for a wallet can be used in another software than the one it was generated with?

Answer: 
The `R` value is the result of EC point multiplication between the `k` value (known as the nonce) and the secp256k1 curve's generator point. It is effectively the public key for `k`. The only way that an `R` value can repeat is if `k` is also the same. Given that `k` is a 256 bit number and is supposed to be chosen completely randomly, `k` should not repeat unless the random number generator is broken.

Considering that `k` is generated at signing time and should be random, we can conclude that whoever chose `k` for those transactions has a faulty random number generator which is either outputting a fixed value or a small value which increases the probability of `k` being repeated. There is no good reason for this to happen, so this error comes from either a faulty RNG or a completely misunderstanding of how ECDSA works.
Because r only depends on the random number k (in addition to curve parameters) and reusing k, as long as the private keys are different, is OK.

Further reading: <https://www.maximintegrated.com/en/app-notes/index.mvp/id/5767>