Added new locale for Poland ;)

[rrakso]

Is your pull request related to a problem? Please describe

Yes it is. It will be great if this experience would be also in polish.

Describe the solution you'd like

I've just added new locale

Test plan

A good test plan should give instructions that someone else can easily follow. Also add a link to your own Messenger experience for your reviewer to test the changes.

Checklist

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.
• [x] The title of my pull request is a short description of the requested changes.
• [ ] I have added the label enhancement to my pull request.

[facebook-github-bot]

Hi @rrakso!

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file.

In order for us to review and merge your code, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

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[rrakso]

I've just signed CLA