Switzerland has four official languages at the federal level, namely German, French, Italian and Romansch, and the main language spoken depends on which part of the country you are in. Individual cantons are free to decide on which official language to adopt, and some cities such as Biel/Bienne and, Fribourg (Freiburg), or Morat (Murten) are officially bilingual. Any part of Switzerland has residents who speak something besides the local vernacular at home, English, German and French being the most widely spoken second languages. Note that you are unlikely to hear Romansch — except in some valleys of Graubünden —, as essentially all the 65,000 Romansch speakers also speak German, and they are actually outnumbered in Switzerland by native English speakers, as well as by Portuguese, Albanian and Serbo-Croatian-speaking immigrants.
Around two-thirds of the population of Switzerland are German speaking, located particularly in the centre, north, and east of the country. Swiss German (Schweizerdeutsch) is not a single dialect, but rather a blanket term for the dialects of German spoken in Switzerland. These dialects are so divergent from standard German that native speakers from Germany can hardly understand them. All German-speaking Swiss learn standard German in school, so almost all locals in the major German-speaking cities (e.g. Zurich, Bern, Basel) and many in the countryside will be able to speak standard German. The many different Swiss German dialects are primarily spoken, colloquial languages, and the German-speaking Swiss write almost exclusively in standard German despite speaking Swiss German. Swiss German dialects are highly regarded by all social classes and are widely used in the Swiss media, in contrast to the general use of standard German on TV and radio in other countries, though news broadcasts are usually in Standard German.
The second most spoken language is French, which is mostly spoken in the western part of the country, which includes the cities of Lausanne and Geneva. Speakers of standard French will generally not have any major problems understanding Swiss French, though there are certain words which are unique to Swiss French. The most noticeable difference is in the number system, where septante, huitante and nonante (70, 80 and 90) are commonly said instead of soixante-dix, quatre-vingts and quatre-vingts-dixas in standard French. All French speakers understand 'standard' French.
Italian is the primary language in the southern part of the country, around the city of Lugano. Swiss Italian is largely comprehensible to speakers of standard Italian, though there are certain words which are unique to Swiss Italian. Standard Italian is understood by all Swiss Italian speakers. The northern Italian language of Lombard is spoken by some as well.
All Swiss are required to learn one of the other official languages in school, and many also learn English. English is widely spoken in the major German speaking cities and therefore English-speaking tourists should not have a problem communicating. In contrast, English is not as widely spoken in the French and Italian speaking areas, the exception being the city of Geneva, where English is widely spoken due to its large international population.