After reviewing the official Microsoft documentation, we found that the email template selection window is different for D365 Sales and D365 Customer Service because the two programs have different requirements.

It is not possible to change the language in an email template in the customer workspace app. This is difficult for us because our clients speak multiple languages.

We can see that several users are finding this annoying and can't work properly as a result. 

See below a link where the problem has been reported before:

https://community.dynamics.com/forums/thread/details/?threadid=f52ab967-c12b-ee11-bdf4-000d3a570dcd