Problems with confirmation mail to subscribers

Issue Summary

I just installed the latest development version, with the latest dev version of mimemail. I have uploaded the (complete) Russian translation for the module. Russian is the default site language. Yet a new user subscribes to receive a newsletter he gets a mail mixed up as a jumble of English text and Russian parameters. In addition, when I look at the mail "Sender" (in Thunderbird) it is a barbarous mix of characters beginning "UTF-8" (maybe an encoding of cyrillic?).
I have looked at Newsletter settings (both general and specific) and everything looks ok. And I cannot find anywhere where I could configure the mail message that gets sent out to users when they subscribe. I see that when cron sends messages they are in site default, so how come the login message does not get sent in site default?