Workaround:
- Manually create the team site from the SharePoint admin center instead of the main or Teams admin centers.
- Set the language for the new site to the same language as the source. Creating the site will create the associated group.
- After the site is created, login and after a few seconds a control will show up in the bottom of the left side panel with the option to activate Teams for the group.
- Migration will be supported because the source and target team/group sites have the same default language.
Alternate:
You may not know that the default language on the root site is different and controlling the language setting for sites created by Group and Teams.
If you are able and open to changing or swap the root site, you can do the following to change what the default language for new Group/Teams sites will be:
- Create a site from the SharePoint admin. The site can't be a hub site or connected with a Group.
- Select the desired language as the default.
- From SharePoint admin center, select the root site then select the Replace site link
- Then enter the url for the site made above to replace the root site.
- The replacement site will be promoted to the root site and the current root site will be demoted to a managed site.