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I think xLanguage is the best. It is based on EMLH but has as advantage that the XOOPS itself (menu's) are also translated or translatable.
Both have allow tags ([en], [/en]) to seperate the content in an article for the languages and have limitations when modules show text extracts, which could lead to unbalanced tags.
Both require a hack (placing an include in one of the core files), so there is no hack free solution.
Other solution is that you use the multisite, which allows eg two subdomains (en.domain.com and fr.domain.com) share the same XOOPS and partially the database (eg users). In fact you get two different sites with their own content.