Is the word irresponsável the same in Brazilian and European Portuguese?

Yes

The word "irresponsável" is identical in spelling, meaning, and grammar in both Brazilian and Continental Portuguese. The only differences lie in pronunciation:

• Brazilian Portuguese: The vowels are generally more open and the rhythm is more "syllable-timed" (each syllable receives a clearer, more distinct weight). The "r" sounds vary by region but are often more phonetic.
• Continental Portuguese: The vowels are more closed or "reduced" (often almost swallowed in unstressed positions). The rhythm is more "stress-timed," meaning unstressed syllables are much shorter, which can make the word sound more clipped or rapid to a Brazilian ear.

Brazilian Portuguese Examples

1. Ele é muito irresponsável com as contas. (He is very irresponsible with the bills.)
2. Não seja irresponsável e use o capacete. (Don't be irresponsible and use the helmet.)
3. Essa atitude foi totalmente irresponsável. (That attitude was totally irresponsible.)
4. Ele é um motorista muito irresponsável. (He is a very irresponsible driver.)
5. Você está sendo irresponsável com seus estudos. (You are being irresponsible with your studies.)

Continental Portuguese Examples

1. Ele é muito irresponsável com as contas. (He is very irresponsible with the bills.)
2. Não sejas irresponsável e usa o capacete. (Don't be irresponsible and use the helmet. — Uses the "tu" conjugation common in Portugal.)
3. Essa conduta foi irresponsável. (That conduct was irresponsible. — Uses "conduta" for a more formal/natural tone.)
4. Ele é um condutor irresponsável. (He is an irresponsible driver. — Uses "condutor" instead of "motorista".)
5. Estás a ser irresponsável com os teus estudos. (You are being irresponsible with your studies. — Uses the "a + infinitive" construction instead of the Brazilian gerund.)