What's this?

When I attach plaintext files to a mail, Thunderbird automatically tries to detect their character encoding from their contents, by the commit:

http://hg.mozilla.org/comm-central/rev/2b9773749c86

However, because the universal (global, generic) detector is always used, Thunderbird often fails to detect character encoding of files. For example, on a Japanese environment, "Shift_JIS" and "EUC-JP" are wrongly detected as "windows-1252".

This addon forces Thunderbird to use localized encoding detector based on the system language, As the result, plain text files will be attached with correct encoding.

This project is currently suspended. See the next section for more details.

Versions of Thunderbird who want this addon

By the commit between Thunderbird 31 and Thunderbird 38, the universal charset detector is removed:

http://hg.mozilla.org/mozilla-central/rev/2f0c68d4d7ca

It is introduced by the bug:

844115 – Remove the "universal" encoding detector (chardet) https://bugzilla.mozilla.org/show_bug.cgi?id=844115

After that, basically Thunderbird 38 and later uses language-specific charset detector. So Thunderbird 38 and later doesn't need this addon. (Of course, this addon will become useful again, if less-effective universal charset detector is re-introduced in the future.)

Steps to test

Note: these steps are just for a Japanese environments. In other languages, they are possibly detected unexpected encodings...

1. Attach samples/*.txt files to a new message.
2. Save it to the Draft folder.
3. Choose "View" => "View Sorce".
4. You'll see detection result for file contents as "Content-Type:text/plain; charset=...." in each header of attachments.

Without this addon, sjis.txt and euc.txt are detected as "windows-1252" unexpectedly. With this addon, they are correctly detected as Shift_JIS or EUC-JP.