Traditionally, in politics, French and German-speakers use their own language and are expected to have at least a passive knowledge of the other. Top-level politicians frequently talk to the media in both languages, no matter where they come from. Italian can be heard in official contexts but Italian speakers are very often fluent in one or both other official languages and have a kind of (unofficial) “junior” position in Switzerland.
A recent anecdote illustrates how this system works: In 2015, the nomination of Guy Parmelin as a candidate for the Federal Council by the UDC/SVP created a lot of debate due to his perceived lack of knowledge of German, to the point that many thought the party deliberately chose two unelectable candidates (Norman Gobbi was unacceptable for other reasons) to force the other parties to elect Thomas Aeschi (Parmelin was elected nonetheless).
That's basically how it has worked for a long time even if there is now a live interpretation service for the lower house of parliament. But not for the upper house nor for the local parliaments in bilingual areas or, to my knowledge, for meetings and other events.
Interestingly, Swiss-German MPs do not use “Swiss-German” (i.e. one of the dialects spoken at home and in other informal contexts in the German-speaking part of Switzerland) in parliament but standard German (in German: Schweizer Hochdeutsch, a slightly different and accented version of formal German).
Finally, Romansch has, as you probably noticed, a somewhat peculiar position. Since a 1938 initiative it was, in the words of the constitution, a “national language” but not an “official language”. It's not used much at the federal level, although its role has actually been increasing just as the language appears to be under threat (cf. e.g. its presence on passports or the 1996 referendum). Virtually all Romansh speakers also know German.
Incidentally, note that in the EU, public parliament sessions and, of course, official documents are indeed interpreted/translated in all 24 official languages but other things (preparatory documents, meetings, work at other institutions, court audiences) are translated in a much more ad hoc fashion.
