FEAT: Add SK and update CS locales

[tomaschyly]

Description

Added new SK (Slovak) localization and updated the CS for untranslated strings.

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• I have run the commands in ./scripts/before_push.sh and it all passed successfully

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.