Add Thai language support to Confluence

Following the documentation regarding translations lead us to the available Thai language package (https://packages.atlassian.com/maven/com/atlassian/translations/confluence-language-pack-th_TH/\) compatible with Confluence version 5.9.4. It is unfortunately too outdated to customize. We are happy to perform the translation by ourselves. Please kindly guide us on how to translate our current installation. Any translation tools available will be immensely helpful.