Resolved questions
Are there accents in Polish language? Can you place the person when he speaks Polish?

The predominant stress pattern is penultimate stress with alternating preceding syllables carrying secondary stress (e.g. człowiekowi [ˌt͡ʂwɔvʲɛˈkɔvʲi] 'human being dat. sg.'). Loanwords complicate this, as they introduce antepenultimate stress (e.g. fizyka [ˈfʲizɨka] 'physics'). However, even loanwords may move stress to the penultimate syllable upon suffixation as in uniwersytet [uɲiˈvɛrsɨtɛt] ('university' with antepenultimate stress) which becomes [uɲivɛrsɨˈtɛtu] (with penultimate stress) when the genitive singular affix [u] is added. Over time, loanwords become nativized to have penultimate stress.

Outside of loanwords, exceptions include:

verbs in first and second person plural past tense, for example zrobiliśmy ('we did') - the stress is on the third syllable from the end

verbs in conditional, for example zrobiłbym ('I would do') - stressed on the third syllable from the end

verbs in first and second person plural conditional, for example zrobilibyśmy ('we would do') - the stress is on the fourth syllable from the end

The explanation for the irregular verbal stress is that these endings are clitics, not verbal inflections: zrobili=śmy, zrobił=bym, zrobili=byśmy. They are remnants of the auxiliary być ('to be'). This can be demonstrated with phrases such as Kogo=ście zobaczyli? (in spoken Polish Kogo zobaczyli=ście?) ('Who did you see?'), where the clitic attaches to the word kogo 'who' rather than to a verb (Kogo zobaczyli=ście?), but kogo maintains its normal stress. However, these endings are in the process of being reanalyzed as suffixes, and as this happens, the stress is shifting to penultimate position in colloquial speech (though by prescriptive grammarians this is still considered an error): zrobiliśmy, zrobiłbym, zrobilibyśmy.