Symptoms
You run a migration for a site that it is in Language A, but when you verify it at your destination, the site is now in Language B.
Error Code
Not applicable.
Details
ShareGate Migrate uses your site settings during a migration. So if your default language is set to Language B at your destination, that is the language that will be used - even if the source environment was in Language A.
Solution
Access your destination SharePoint site settings, and switch the default language to that of your source.
You can see more on this issue here, and access Microsoft's detailed instructions on how to resolve this.