Multilingual websites

We have extensive experience building multilingual sites – mostly English/Welsh bilingual but also including sites with as many as four languages. Whichever of the available solutions we were to choose for this project it would need to would meet these minimum requirements:

1. A simple, intuitive editing experience that minimises duplicated effort for site editors.
2. A well supported project with a large user-base and regular updates (this also applies to any third-party plugins).