I may be wrong but there are nearly 6000 languages spoken in the world today and they are divided in some main languages around 6 or 7 and rest as secondary languages.
Top five most speaking languages are Mandarin, Spanish, English, Hindi & Arabic and Mandarin have coverage of 14% of world population (of Couse due to population), for more information about the languages, you can Visit Wiki page https://en.wikipedia.org/wiki/List_of_languages_by_number_of_native_speakers
Moreover, the size of countries and populations don’t necessarily account for numbers of languages, in New Guinea almost 452 languages are spoken by a people of only 3.5 million.
Before travelling to your desired destination, make a note of language spoken at that place and check your comfort level against those languages and don’t Panic, if you don’t have any comfort level in any language, as a smile can go a long way, even mid of the people you share no language with.
Having said that, just learn some world of language spoken at your destination and this can show a lot of new doors.
Moreover, you can use some Mobile apps as translator which can work as a Guide on your travel.
The next big thing you should know about before planning a travel is Time Zone.