link in default polish homepage needs to be changed

Thanks for reporting this bug.

Are there any Polish-language documentation sites that we could link to instead of the English-only help.ubuntu.com/community?

There is https://wiki.ubuntu.com/PolishDocumentation but it's incomplete and very outdated. For now help.ubuntu.com/community should be linked. You can add " (po angielsku)" after both "Oficjalnej stronie dokumentacji Ubuntu" and "dokumentacji opracowanej przez społeczność" to indicate that they are english links.
BTW: you can change words "Oficjalnej" and "Stronę" to lowercase to make it grammatically correct.

I've subscribed the polish translators to this bug, they can state their opinion on this bug.

Is it possible to fix via Rosetta? Where's the template for this page?

The point making "Oficjalnej" lowercase is valid, however changing the link is debatable.

On one hand this is the best a user can get in Polish.

On the other, if someone starts to maintain the PolishDocumentation website, he/she will be left out in the cold.

An ideal solution would be to add both links to that page, with indication that one of them leads to an English webpage.

This page also needs a thorough rewrite to comply with our policy not to address the user directly. I'll do this if someone points me to the source/template. dpkg -S isn't helpful.

In kubuntu-docs there is a kubuntu-docs-index template, if there is an analogical template in ubuntu-docs then it is missing in rosetta.
Compare
https://translations.edge.launchpad.net/ubuntu/gutsy/+source/ubuntu-docs/+translations
and
https://translations.edge.launchpad.net/ubuntu/gutsy/+source/kubuntu-docs/+translations

Tomasz - the startpage is currently translated manually so if you send me via email an amended html version of the page, I will include it in the package.

In the future we hope for translations to be available through Rosetta. I'll close the bug on the basis of your comments about changing the link being debatable and we can continue by email.