I’ve written an EE plugin that will let you change language localization settings from within templates. I call it the ‘template_language’ plugin. It’s attached to this post as ‘pi.template_language.txt’. To use the attachment (save it into your plugin folder and) rename it to pi.template_language.php.
It can be used to:
(A) Override any site wide language localization settings and any user control panel language preferences for a CURRENT template/page.
(B) Override any site wide language localization settings and any user control panel language preferences for FUTURE templates/pages (that a user will visit after the current one). This works only for ANONYMOUS (not logged in) users. I use it to set the language for the “user message template” (such as the “mailinglist subscription message” etc.).
Please try it out and give me your feedback about bugs etc. I plan to add the final version to the pMachines list of plugins for EE if you like. Thanks.