Messaging plugin i18n broken, and input not verified

Hello,

I try to translate messaging plugin, and i have internationalisation and input handling problems.
When i translate this plugin some messages not able to translate (for example notification email message strings are translated, but content not processed from .po file. or Message(s) Sent message appear as default lang.
Also problematic:
Usernames in WP able to contains space like "firstname lastname" but user input handler can't accept these names (i can send messages from these users, but other user can't replied on these messages) When i try to mask usename vith quotes (' and ") in username input line, i see the double quote may not escaped well in input usernames.