Hi,
Content in Dynamics 365 for Marketing does not support dynamic localization. For all entities, a single record must be created for each language and / or localization that is supported.
You can create a series of marketing emails with different languages.
They can be distinguished by the Language option under the Summary tab.

Here are steps to create a series of emails.
- Create a Marketing Email from a Blank Template.
- After saving the Marketing Email, click the Save as Template button in the command bar to create a new Marketing Email Template.
- Change the Language of the Marketing Email Template to the desired Language and make modifications.
- Return to the Marketing Email created in step 1 and follow steps 2-3 again to create Marketing Email Templates for additional localizations.
Create a customer journey after going live these emails.
Set customers from the same nation into a segment.
Set different segment as audience for different swim lanes in the Customer Journey.

Then choose mail in the corresponding language to send to customers in the corresponding nationality.
If this helped you, I'd appreciate it if you'd mark this as a Verified Answer, which may in turn help others as well.
Best Regards,
Nya