I work on a large/popular open source project and the one thing we get requests for more than anything else is multilingual support (which we'll be adding in th

I work on a large/popular open source project and the one thing we get requests for more than anything else is multilingual support (which we'll be adding in the next major version). Everyone seems to think it's so easy to add with the inclusion of one language file to translate the system. While it's true that this can be used to translate the core system (and is probably what we'll do) our software is designed to deal with large quantities of user-generated content, so we also need ways to support multiple translations of that content, handling fallbacks if the translations don't exist, switching between them on the fly, search indexing, making our UI fluid enough to accommodate different lengths of text in navigation, etc. The list goes on. None of this is particularly difficult, but there is a lot to consider that, judging from our user base a lot of people (many of which are developers themselves), just don't think of. Proper multilingual support can be quite tedious.