I18n should no longer be creating null attributes

[rorticus]

The following has been addressed in the PR:

• [x] There is a related issue
• [x] All code has been formatted with prettier as per the readme code style guidelines
• [x] Unit or Functional tests are included in the PR

Description:

Fix for i18n adding lang="null" attributes, making a11y tests fail!

Resolves https://github.com/dojo/widget-core/issues/904