Excuse me, do you speak my language?
Some of us use email to communicate with people we never met before. Customers, clients, users, providers, and so on. Most of the time, we will communicate in English, the lingua franca since the Beatles, Monty Python and Douglas Adams conquered the world. I'm not, as you might have guessed from my broken English, a native speaker, nor are all of my peers. Maybe we were better of speaking another language both sides know better. But how would we signal our counterpart which languages we know, other than by cumbersome explanations?
Accept-Language to the rescue
Accept-Language is an optional email header, that can be used to declare, which language the sender is able to accept. E.g. if I'm able to speak Afaraf, Abkhazian and English, I would send an email with Accept-Language: aa, ab, en. The receiver of the email would now want to reply in one of the three languages. The order reflects the preference. Here, I would prefer Afaraf over Abkhazian, Abkhazian over English.
How to apply this in mutt?
To see the Accept-Language headers in received email, just add the following line to your ~/.muttrc: unignore Accept-Language
You can colour the line red, if you don't know any of the senders languages, and green, if you know at least one of them:
color header red black ^Accept-Language:
color header green black ^Accept-Language:.\*(aa|ab|en)
To send your own Accept-Language header, add this line to your ~/.muttrc: my_hdr Accept-Language: aa, ab, en
How to apply this in Thunderbird?
To see the Accept-Language headers in received email, just add the string Accept-Language to the configuration variable mailnews.headers.extraExpandedHeaders, which is a space separated list.
To send your own Accept-Language header, add a new string configuration variable mail.identity.idN.headers where N must be replaced with a number, identifying your email account in Thunderbird. If you have only one account, it is probably 1. Set this mail.identity.id1.headers to accept-language. Case matters. Create a second string configuration variable mail.identity.idN.header.accept-language (again replacing N, e.g. mail.identity.id1.header.accept-language) and set it to the complete header string with comma separated list of the languages you know using the ISO codes, e.g. Accept-Language: aa, ab, en.
Note, that the information what languages you accept, is transferred in an email header. OpenPGP will not
encrypt this information. If you are using an anonymous or pseudonymous email account, the presence of the header or its content might help others to reveal your identity.
PS: Please do not write to me in Afaraf nor Abkhazian. I took the languages as example because of their nice ISO codes.