German is not a Latin language, rather it is a West Germanic language, like English. Polish is not a Latin language either, but a West Slavic one. Latin belongs to neither of these groups, but to the Italic language family. However, all four are IndoEuropean languages, so certain similarities, such as cognates, are to be expected. Loanwords also abound: Latin had a significant influence on Polish, for example, and was for a time the official language. Polish also has a number of calques from German - phrases translated literally. Yidish (something of a linguistic mixing pot, and owing much to Germanic) has also had an impact on Polish - paradisus Iudaeorum and all that. German also has a number of Polish loanwords.

Poland was the centerpiece between Russia and Germany for a very long time so they adapted alot from both cultures forming their own. You could ask if russia and slavic countries are all majority Christian Orthodox and neighbor Poland why are they overwhelmingly Catholic? Because Germany has had close ties to Catholicism. So in poland's case, if it's not german influenced, its usually russian influenced, or vice versa.