This is a pdf + code containing the instructions and the BIP39 list (English in pdf and English and Japanese in code) for offline generation a full BIP39 24 word seed (the words' lists are taken from https://github.com/bitcoin/bips/blob/master/bip-0039/bip-0039-wordlists.md). The first 23 words are generated using paper and dice, and the 24th word is generated using the script 24thword.py.
Print the pdf, grab a pen, a pocket calculator (optional) and some dice and generate the first 23 words.
To determine the final 24th word, on an OFFLINE machine, edit rolls.txt and replace the words with the 23 that you chose using dice. Then run:
python3 24thword.py
You will be given a list of 8 valid 24th words. Pick one (eg by rolling 3 dice using and using the method above to get a number between 1 and 8), write your chosen word with the other 23. This is a valid wallet seed, and you can use it with Electrum or some other wallet application.
If you don't have an airgapped (permanently offline) machine, you could use seedsigner.
For more information you may check: https://learnmeabitcoin.com/technical/mnemonic
To receive money to the wallet. You'll need an address (derived from your xpub). To send, you'll need your private key. The keys you'll need to do both of these things can be derived using an offline version of the page https://iancoleman.io/bip39/
The code that you generated needs to be stored in a secure way, here's a video of one (of many) possible methods:
Code for 24th word was based on avsync/bip39chk
GPL 3.0