Honestly? This is a square wheel. So by all means go and reinvent it, but it'll be extremely painful to convince anyone to implement your new standard, which is basically why BIP-39 is used by everyone except electrum.

> So yes, you can use anything custom, but you cannot ever lose it

This is like make my own cypher, what is a really bad idea.

“**Don't try to reinvent the wheel**” rule

Fenix

is it a good idea build a wallet like that?

So yes, you can use anything custom, but you cannot ever lose it. It's not a recommended use because text has encoding of its own, especially when using non-ascii characters. If you make something custom, drop the 

byte entropy -encode-> words
   |
   \-hash-> BIP-32 seed

Stacker Saloon

saloon

> is it a good idea build a wallet like that?

Not really. It's recommended against [in the BIP text](https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki#wordlists)

> > Since the vast majority of BIP39 wallets supports only the English wordlist, it is **strongly discouraged** to use non-English wordlists for generating the mnemonic sentences.

BIP-39 since recently also states under [shortcomings](https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki#shortcomings):

> > * Generated seed depends on the wordlist that was used for the mnemonic. Because the "mnemonic to seed" process uses the mnemonic sentence directly rather than the original entropy, translating the mnemonic to a different wordlist necessarily creates a completely different seed. This is not an issue if you only support the English wordlist, as recommended above.

So yes, you can use anything custom, but you cannot ever lose it. It's not a recommended use because text has encoding of its own, especially when using non-ascii characters. If you make something custom, drop the `hash(words)` and instead do.

Generation:

```
byte entropy -encode-> words
   |
   \-hash-> BIP-32 seed
```

And restore:

```
words -decode-> bytes -hash-> seed
```