Forum OpenACS Q&A: Response to Internationalization of OpenACS
For the templated modules you just need to create a template under the templates directory and call the template from within the page you're doing your queries and tcl coding. Polls, news, ecommerce are templated.
For the other modules, the only way to do different languages would be a) template-enable them, b) change the embedded HTML code within the tcl pages. Option b is easier but does not scale since when new versions of ACS come out, you'll have to merge your changes, which means you'll have your own version of ACS.