I think one of the most important things about a secure master password, is not to confuse yourself, or the user themselves. A lot of times we try too hard to play with bunch different characters and unknowingly get ourselves into trouble.
I use Japanese characters as an extended protection for my password. I usually have my Japanese chars stored somewhere easy to access (like in Bitwarden itself, Google Pswd Mgr, Apple Keychain etc.) and just copy and paste it into the master password field and then type the traditional password. For example: “MySuperSecretASCIIPassword_123” + “[Pasted Japanese Characters]”. Usually copying and pasting UTF-8 characters reduces chance where I am gonna mess up the UTF-8 characters. Plus I don’t really care if a friend knows the Japanese part of the password, because they still don’t know the ASCII part of the password nor they have access to my encrypted vault files that give them access to try to break it with unlimited tires.
The reason I decided to use UTF-8 character sets is because of what happened to Lastpass, in the worst case, same thing happen to BW. I want my password able to with withstand brute force attack and future-proof, since there is no way for a user to delete their encrypted vault from the hacker’s hand. A 16 chars ASCII random password is considered as safe with today’s standard, but given a hacker 50+ years and furutre technologies to break it open, would 16 chars ASCII random generated password with PBKDF2 still as safe? Sure, the user can change their login password over a weekend, but not everything is changable, like let say someone stores their social insurance number in BW. Once the vault is break open, the hacker will have access to a lot of personal data that is not changable.
The hacker who stole Lastpass vaults, are not likely have access to users’ Google/Apple account at the same time, so if the user setup their password like this, the hacker will have a much tougher time to break their vault open. And most of the users are probably not worthy enough for the hackers to perform a sophisticated social engineering attack on.
As for traveling, yes, no one should unlock their vault in a device that is not trusted. I usually bring my personal devices for traveling instead of internet cafe. There is just too much risk to login to the BW vault on an untrusted device. The bad actor can export the vault without the user’s knowledge once it is unlocked and/or just remotely take away the control and the user won’t even be able to lock their vault. If bringing personal computer is not possible, the user should create a temporary BW account and share only a limited set of passwords they need for travel purpose.
Above are just my thoughts on Best Practices on Master Password and where I am coming from for using UTF-8 passwords.
Again I elaborate this one more time, in case someone did not ready previous posts. Please backup your vault in plaintext and setup proper emergency access before trying anything I mentioned above.