How do you maintain your multilingual websites ?

• Do learn and understand the differences between Unicode, Utf-8, character encoding etc. before you get into all of this stuff
• Make sure your database uses the right Collation (like in MySQL's case)
• Keep your translations in en external file, make sure it's saved in the right format, or in the database - in the latter case make sure your database can store/read/write them properly using the client libraries that you have access to
• Have a "source" for a translation that is then translated into different languages, including the language that the "source" language is in - that way you can always fix mistakes in the original wording
• Decide for an offline-approach - translating using textfile - or an online-approach - using a backend system that enables you to translate your content
• Think about exporting your content to any of the known translation formats (usually XML or HTML) so professional translators from ProZ.com etc. may use them in their favorite translation tools
• Consider exporting your content to Excel as well, this greatly speeds up bulk translations for translators that don't use any tools or prefer to work offline
• Keep in mind that you need placeholders, like ${username} - BUT: they tend to get you in trouble when browsers render them though, so there's some learning needed there as well
• For websites: check out the following HTML-related tags: unicode-bidi, direction, rtl, ltr etc.
• Never EVER go for Google Translate :-)

Those were just a quick ones I came up with out of the top of my head. We really had to go the hard way when we implemented 7 languages on http://www.salambc.com (@Admin: sorry for the blatant advertising, please censor it if it's not permitted here) and had to learn that even RTL (right-to-left) languages such as Arabic, Urdu or Persian do not adhere to the same set of rules. It's worth the trouble though.

P.S: Ping me if you need a skilled English <--> Arabic, Persian, Turkish etc. translator.