Update messages.po

I fixed some imperfect points here.

Besides, the Vnm interface still has some problem as below:
1. On the Canon site, the main menu's titles are having large space. It should be short space like the Dictionaries site. (For example: "Trang chính". Not "Trang   chính"

2. The Vnm interface should has full name as: "Tiếng Việt" instead of "Việt". And once being inside it, the menu should be: "Tiếng Anh" instead of "English"; "Tiếng Pháp" instead of "Francais"; "Tiếng Hoa (Đài Loan)" instead of 中文 (繁體); "Tiếng Hoa (Đại Lục)" instead of 中文 (简体)
Merge pull request #4 from quytinh/master

Fixing Vnm interface