to_entropy() cannot read the japanese mnemonics to_mnemonic() writes

[fametrano]

Mnemonic("japanese") joins words with U+3000, the ideographic space
(#L73,
#L210),
as BIP39's Japanese vectors do. to_entropy and expand split on " ", so
they see a single word: the first raises, the second returns the sentence
unchanged. check accepts it, because it normalizes first and NFKD maps
U+3000 to U+0020.

The README's own steps are the reproduction. On master, python 3.12:

>>> from mnemonic import Mnemonic
>>> m = Mnemonic("japanese")
>>> words = m.generate(strength=256)   # README: "Generate word list"
>>> m.check(words)
True
>>> m.to_entropy(words)                # README: "calculate original entropy"
Traceback (most recent call last):
  ...
ValueError: Number of words must be one of the following: [12, 15, 18, 21, 24], but it is not (1).

That block is a doctest, and passes as written on master; with this patch
applied it fails, because to_entropy then returns the entropy. On
vectors.json, check accepts all 288 mnemonics while to_entropy fails
on all 24 Japanese ones and none of the other 264.

#110 fixed this by splitting on self.delimiter; it was merged as
71cf5203 and reverted as df3e1500 for failing CI. That direction cannot
work in check, which normalizes before splitting: after NFKD there is no
U+3000 left to split on, so every Japanese mnemonic fails validation
instead. Hence any run of whitespace, read after normalization — which is
what detect_language already does.

The fourth changed line applies the same rule to to_seed, whose NFKD-only
reading silently stretches a different seed out of the input check
rejects: a leading space, a trailing newline, a tab. If that is unwanted,
drop it along with the last assertion of test_whitespace_runs; the other
three still fix the Japanese bug.

Compatibility: all 288 vectors are unchanged — test_vectors asserts
mnemonic, seed and xprv for each, and passes. No input check accepts today
derives a different seed; what changes is input it rejects, which now
derives the canonical one. The passphrase is untouched, its whitespace being
part of the secret.

CI, since #110 was reverted for failing it: python tests/test_mnemonic.py
is OK on python 3.8 through 3.14 and on pypy 3.11, and black --check,
isort --check-only, flake8 and pyright report nothing on
src tests tools.

Written with machine assistance and reviewed against master b57a5ad
before filing. Found while checking btclib's BIP39 reading against this
implementation: btclib-org/btclib#258.

🤖 Generated with Claude Code