Fixes in localisation

3385ffdd51f044a9e239fad32f596c9939701d5f
mail_charset is not set anywhere, so email goes without default charset and got incorrect quoted-printable string in "from" field in case of unicode string. Hardcoding UTF-8 right here converts good string in ALL languages.

c0bf75c362feae2dbbb1b3b0b0ca4c72d3a3c86e
In case of first opening login page textdomain is set, but for page_forgot and page_register index.php has own case clause, where no textdomain set, so gettext not working . This ugly fix makes localisation start working at all theme pages.

8f0ba9d0a57400fb55f8695775c96e40e791a202
After inclusion plugin pages textdomain should be switched to themes for translation strings "Home", "Logout", "User configuration" and "Preferences" on plugin pages. This commit makes all menus get translated