|Many CMS type site (e.g PHP nuke) code the "content" of the pages with placeholders and pull the actual text from "language" files. This would require a server-side language such as PHP.|
If you ONLY have to have 2 languages, then just sticking with flat HTML pages is an option. But, even with two languages it can still be problematic when updating. If you were to have more than two then you definitely need to look into a server-side language.