If my interpretation of your question as " except for English, what other languages are most often used for communication between people of different nations so that the language used for communication is foreign for all parties ", then the answer is the following:
In many areas of the world there are other so-called "auxiliary languages" that are used for communication, trade, negotiation between people of different nations: Russian is still spoken in many countries of the former Soviet Union and their neighbors, as well as around the globe for there are many migrants with Russian roots everywhere.
As a native speaker of Russian
I used it freely in Ukraine, Poland, Bulgaria, Czech Republic, but also on daily basis in Germany and US.
French is the second language in many countries in Africa, in Canada etc.
It was the first language that was widely adopted for international use ( lingua franca ) and used like language of international post etc.
It is still in use as primary language in Olympic Committee and other international organizations (UNO).
Mandarin Chineese is used a lot in China to level the ground between different dialects and language learners.
Last, but not least, Esperanto is a the most successful planed language (=constructed language) that was used by many millions of people during its peak and still in use by thousands of people around the globe.
languagelearning.stackexchange.com/users/1938/Alexander Galkin
Please check Wikipedia's List of languages by number of native speakers .
Mandarin is the biggest language, as expected, followed by Spanish, English (which we exclude for this question), Hindi, Arabic, Portuguese, Bengali, Russian, ...
You should not make too many assumptions about the foreign language skills of native speakers of big languages.
When you are in a big tourist location in China, you will always find someone who knows (some) English, but once you move off the beaten track, it is better to know Chinese.
If Chinese looks too daunting, then Spanish and Portuguese are good choices.
However, is the number of speakers your main motivation for choosing a foreign language?
You should also consider the countries you would like to travel to or the cultures with which you would like to interact.
See also The #1 Key Element to Choosing a Language to Learn , which discusses several things that can motivate you to pick up a foreign language.
languagelearning.stackexchange.com/users/800/Tsundoku
Based on this wikipedia page , I would say your best shot would be to pick a language based on which country has the smallest number of English speakers, then figure out what the most popular websites/messaging apps in those countries are.
For example, this website claims that the most popular messaging app in Russia is WhatsApp.
I don't know much about WhatsApp, but assuming it's similar to apps such as kik and telegram, it'll have specific groups that you can join, and I'm sure you'll be able to find one with Russian speakers who know no English.
languagelearning.stackexchange.com/users/1969/Jake H
I'd use the same list that Christophe Strobbe referenced, but with a few corrections.
As he stated, the top 10 most spoken languages in the world (excluding English), ordered by native speakers, are Mandarin, Spanish, Hindi, Arabic, Portuguese, Bengali, Russian, Japanese, Punjabi, and German.
It isn't necessary to learn all of these languages to be able to communicate with their native speakers
; keep in mind, this list is based on the number of native speakers only.
Many people who speak one of these languages speak another as well, meaning it isn't necessary to learn all of these.
For one, after several hundred years of British colonialism in India and Bangladesh, the teaching of English in schools is emphasized, and thus most Indians or Bangladeshis born within the last 60 years are fully fluent in English, if not at least mostly literate.
Because of this, Hindi, Punjabi, and Bengali really aren't vital to know; you can communicate with most, if not all, Hindi, Punjabi, and Bengali speakers with just English.
In a nutshell, the answer to the question What are the most common languages among people who DON'T speak English? is the first list I provided.
However, if you want to make a better decision and choose langauages whose group of speakers will not overlap with each other, you should go with this better revised list:Mandarin, Spanish, Arabic, Portuguese, Russian, Japanese, and German.
The easiest to learn out of this list for an English speaker would be Spanish, Portuguese, and German.
languagelearning.stackexchange.com/users/91/fi12
I'd suggest looking at list of L1+L2 speakers combined ( https://en.wikipedia.org/wiki/List_of_languages_by_total_number_of_speakers ).
Top five would be Mandarin Chinese English Hindustani Spanish Arabic Considering that English and Spanish are pretty close to each other, learning both instead of learning one or other would be a pretty simple first step.
Portuguese would be another somewhat near language to learn, even though it's not commonly used L2 language.
Portuguese is mostly worth learning if you intend to interact with native speakers.
French is another language that has pretty massive L2 speaker population and it's pretty close to English and Spanish, too.
Selecting between Mandarin Chinese, Hindustani and Arabic depends on who would you like to interact with.
None of those languages are near each other so learning one of those does not make learning another one easier.
I would assume that most speakers of Mandarin Chinese, Hindustani and Arabic, that know at least one another language, will speak English.
languagelearning.stackexchange.com/users/3480/Mikko Rantalainen
Im Spanish,
Its spoken in south america, central america, some islands of the pacific (filipinas for example) and Spain of course (my country, its in Europe)
, this is a advantage over chinese because you can know different cultures and countries.
About the ratio between native speakers who speak English, I go with Flimzy.
I think the majority of Mandarin speakers don't speak English.
But unless you find yourself in rural China, you won't ever encounter those people, either.
The absolute number of language speakers is usually a very poor metric for the usefulness of the language.
–
Flimzy♦ Aug 9 at 13:31 Spanish may have more non english speakers with internet access.
languagelearning.stackexchange.com/users/2629/arv187
My aim in language learning is to communicate with the most people.  I want to learn a new language and thought to learn Mandarin Chinese, because it's the most common language. But I figured if a lot of people who speak Mandarin already speak English then it would be better to learn the most common language among people who don't speak English. I suspect it's still Mandarin, but I just wanted to make sure. So, what are the most common languages among non-Anglophones?
What are the most common languages among people who DON'T speak English?
languagelearning.stackexchange.com
<english><language-comparison>
languagelearning.stackexchange.com/questions/2019
languagelearning.stackexchange.com/users/1970/Chimaera Phantasma
The most commonly spoken languages in order are Mandarin, Spanish, English,, Hindi, Arabic, Portuguese, Bengali and Russian. The most common languages among non- Anglophones are Mandrin, Spanish, Hindi, Arabic, Portuguese, Bengali and Russian
The most common languages among non- Anglophones are Mandrin, Spanish, Hidi, Arabic, Portuguese, Bengali and Russian