Thank goodness! After several days of effort, researching, studying documentation, and reading code, I finally managed to recover all of my bitcoins. The core issue was indeed related to the mnemonic phrase. Let me recap the key points.
Mnemonic phrases in different languages cannot be directly converted. I had mistakenly believed that I could convert mnemonic phrases between different languages using the word list index provided by
https://github.com/bitcoin/bips/blob/b1791c24aa163eb6578d0bfaadcf44997484eeaf/bip-0039/bip-0039-wordlists.md.
This turned out to be the crux of the matter. Since most wallets only support English mnemonic phrases, and mine was in Chinese, my attempts to replace it with English words using the index and trying different derivation paths were unsuccessful. Upon revisiting the
https://github.com/bitcoin/bips/blob/b1791c24aa163eb6578d0bfaadcf44997484eeaf/bip-0039.mediawiki mnemonic specification, I realized that the index was only meant for checksum verification. The actual seed calculation involves treating the original mnemonic phrase as a string. Identifying this core issue, I used the
https://github.com/iancoleman/bip39 (offline) tool to convert my Chinese mnemonic phrase into the BIP032 standard with a custom derivation path (m/0'/0). I saw my addresses were there, and I knew success was just one step away.
Using the Electrum wallet, I imported the master public key address generated by
https://github.com/iancoleman/bip39. However, I still couldn't see the balance, which was puzzling. After examining Electrum's source code (
https://github.com/spesmilo/electrum/blob/586d3a4361f5dbb9ce9ffdfdfeb276664b5bbfaa/electrum/bip39_recovery.py#L51), I discovered that it automatically adds /0 to the derivation path. Understanding this, all I needed to do was fill in the derivation path as m/0' in
https://github.com/iancoleman/bip39, enter the corresponding public key (xpubxxx) into Electrum, and finally, I could see the transaction history. With this, I've successfully recovered the bitcoins I lost.
I believe there are probably many others like me who think that mnemonic phrases in different languages can be converted. Moreover, most wallets on the market only support English mnemonic phrases, and this is the core issue.
Here, I express my gratitude for all the help provided. By sharing my experience, I hope to assist more people who might encounter similar challenges.