Although you can build your course in any language, the Thinkific platform including navigational buttons and menus is only available in certain languages and right now. We don't support right to left languages such as Arabic and Hebrew.
If you have a developer available and want to customize your site to hard code your desired language, it would need to be done through the code on your site. We do not provide support for code customizations, however we have some wonderful freelance web developers on our Thinkific Experts page who you can reach out to if you need. Many course creators also use upwork.com or fiverr.com for hiring developers. You can see more details on editing theme code here: Custom Themes (For Developers) and editing the theme code is available on our Pro plan and higher.
If you would like to add your vote to this feature request, feel free to reach out!