Ahhh... Wikipedia :).

OK, so please refer to this one:

https://en.wikipedia.org/wiki/Kashubian_language

Many scholars and linguists debate whether Kashubian should be recognized as a Polish dialect or separate language. From the diachronic view it is a Lechitic West Slavic language but from the synchronic point of view it is a Polish dialect.[12] Kashubian is closely related to Slovincian, while both of them are dialects of Pomeranian. Many linguists, in Poland and elsewhere, consider it a divergent dialect of Polish. Dialectal diversity is so great within Kashubian that a speaker of southern dialects has considerable difficulty in understanding a speaker of northern dialects. The spelling and the grammar of Polish words written in Kashubian, which is most of its vocabulary, is highly unusual, making it difficult to comprehend also written text by native Polish speakers.[13]

Like Polish, Kashubian includes about 5% loanwords from German (such as kùńszt "art"). Unlike Polish, these are mostly from Low German and only occasionally from High German.[14] Other sources of loanwords include the Baltic languages.

As you may see, this subject isn't trivial. If we considered Kashubian as a separate language I would say it is similarly difficult (or easy...) to understand to me as Slovak. But for other ears it could be more difficult.

@Alan - man, you have over-simplified complicated topic. 

Kashubian is treated by language specialists as a regional dialect of Polish, it's been that way for ages. Some of them started arguing that it is a separated language but this thing is still under discussion. The same applies to Silesian, it's more like a regional dialect than anything else.

The differences are mainly related to the culture and moreover, a term 'minorities' can also be a subject to discussion.

So, please don't mistake people saying such things.