Sometimes when you click on New Language it shows Template Missing as shown in the image below:
This is the issue when the plugin or theme doesn’t already has a template created for translation.
Click on Create Template button
Again, click on Create Template.
Once the template is created, you can now add the language and translate your plugin/theme easily.
When you create a new language, there are sometimes when user is not able to find some strings from the theme/plugin in the strings table. Or they get the notice message like “Translations don’t match template. Run sync to update from plugin-name.pot”
This is because the plugin or theme has old template/pot file. You can simply click on sync button as shown in the image below: