english vs others languages

almost everybody can talk english. but why? a few years ago everybody was peaking any other language then english.
now, everyone speak this language. a lot of people prefer to talk english in stead of other international languages like french, german, russian and others. but in same time in countries like Ireland they renounce at their own language and speak english. i saw a litle guy that told me that he knows more polish then irish, even he was in Ireland. Is a good thing to know a laguage that can connect as more then Nokia, but shall we renounce at our native language?
As many language known better for yourself. It's not a burden on your shoulders, but how can i say something to somebody and made myself understood only by that person.
I speak now English, Russian, Romanian and I learn French.