Enforced utf-8 encoding on imported files

[elyang0214]

Description

Fixes #4693.
To address the bug outlined in issue #4693, we added a utf-8 encoding argument to the import_files function in the commands.py file.

To Do

• Documentation. (If you've add a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• Changelog. (Add an entry to docs/changelog.rst near the top of the document.)
• Tests. (Encouraged but not strictly required.)

[sampsyo]

Thanks for getting this started! Here are a couple of small suggestions about the documentation.

[sampsyo]

Looks right to me! Many thanks!!