Multilingual User Interface (MUI) and multilingual page translation are SharePoint features that allow your users to view your sites in their preferred language.
Multiliginaul User Interface (MUI)
MUI allows your users to see and use SharePoint site interfaces such as site navigation, site title, and site description, in their preferred language rather than the default language used when the site was created.
You migrate a site with an MUI and it only renders in one language at the destination.
The ShareGate migration tool does not preserve the language settings or translations of your sites. The destination site will use the default language of the destination tenant or farm.
Communication site multilingual pages
In SharePoint, when you create a communication site page in your default language, you can manually create a corresponding page in a chosen target language for users who prefer that language.
You migrate translated pages from your source communication site and the links relating the content are lost.
The ShareGate migration tool does not fully support multilingual page translation. The destination site will contain your translated pages under the language folder in the SitePages library; however, the original pages will no longer have the links that point towards these translated pages.
SharePoint will invite you to recreate the translations but it is not possible to link back to your existing translations.