Once you settle the question, "Should you learn another language?"
the next logical question is, "What other language should you learn?"

Please tell me what are the best suggestions for additional languages,
based on criteria such as: what are the most widely spoken languages
in the US and in the world, what languages do most people have in
common, what are the languages considered to be best and most
rewarding to learn based on their similarity with other language and
word roots, what languages are spoken in the major economic powers,
etc.

It's an open-ended question, so have fun and points for creativity.
Answers in the form oof lists, with references to sources especially
appreciated.

Dear R W McCauley, 

As you stated, there are several ways to determine what is the best
language to learn. You mentioned several indicators:
- How widely is the language is use
- Most similar to other languages
- Spoken in major economic powers

Wide usage of the language
--------------------------
In the United States, 28 million people speak Spanish as their mother
tongue. Others speak a variety of languages (2 Million speak Chinese,
1.6 million speak French, incl. Cajun, and 1.3 million speak German;
1.2 million speak Tagalog and 1 million speak Vietnamese), as you can
see in the US census:
<http://www.census.gov/population/cen2000/phc-t20/tab05.pdf>. 

However, the United States is not representative of the rest of the
world, where English takes hardly first place:
The site Krysstal has some statistics that would help you divide the
languages into groups, including charcter type:
"The 30 Most Spoken Languages of the World" 
<http://www.krysstal.com/spoken.html> 
The top 10 are: 
Mandarin Chinese, with 885 million speakers; Spanish, with 332 million
speakers; English with 322 million speakers; Arabic with 235 million
speakers; Bengali with 189 million speakers; Hindi with 182 million
speakers;  Portuguese with 170 million speakers; Russian with 170
million speakers;  Japanese with 125 million speakers; and German with
98 million speakers.

To conclude this part - it is best - demography wise - to learn
Spanish (most widely spoken after English in the US), after which,
Mandarin or Arabic would probably come.

However, and here we get to the part about the similarity of
langauges: both these two have unique alphabet (which you'll have to
learn), as well as non-European grammar.


Most similar to other languages
-------------------------------
Several languages are known to share their roots with similar
languages of the same family, making it easier for those who
understand one language, to understand others:

Hindi - whereas many words are shared with other Hindu-Iranian languages

Russian - whereas many roots, grammatical forms and words are shared
with other Slavic languages

German - shares with other Germanic languages (incl. English): Dutch,
Scandinavian languages, etc.

Spanish - shares with the other Romanic languages (Romanian, Italian,
French, Portuguese).


Major economic powers
---------------------
The G-8 (Group of Eight) member nations are: 

Canada, where English and French are spoken (as well as Native
American languages).

French Republic, where French, as well as several local languages, is spoken. 

Federal Republic of Germany, where German, as well as some
local/minority languages, is spoken.

Republic of Italy, where Italian, as well as some local/minority
languages, is spoken.

Japan, where Japanese is spoken. 

Russian Federation, where the main spoken language is Russian.   

United Kingdom of Great Britain and Northern Ireland, where English is
the main language (alongside some local/minority languages)

United States of America, where English is the main language, and
whose language construction is discussed seperatedly .

European Union - Official languages: 
Danish  
Dutch  
English  
Finnish  
French  
German  
Greek  
Italian  
Portuguese  
Spanish  
Swedish  
(SOURCE: New EU languages: The new official languages of the European
Union, <http://www.traduguide.com/EU-languages/new-EU-languages.asp>).

It seems that if economic powers are considered, French might be the
best language to learn, alongside English (as well as Japanese or
Mandarin).


Is that an Answer?
----------------
No. 

In my opinion, all the indicators you've mentioned help us to
understand which languages have importance in the world, because of
their expansion, or because they are a Lingua Franca, but does not
explain, which language is the "best" to learn.

"Best" is not only a matter of efficiency. It is also a matter of
other components: which language is the one where you could
communicate with a culture that fascinates you? Which is the one where
you could help the most people? Which is the one, where there is a
shortage of translators (for example: The US Government sought
Vietnamese speakers in the 1960s, eventhough this is not a common
language); which one is connected with your heritage, your culture and
your identity? And if it is only a business question - where you want
to make your business and with whom?

These are not easy questions at all. 

Here are several advices: 

"Frankly, the question can't be answered. That is, there's no single best
language, in economic terms, for a speaker of English to learn. Obviously,
English fills that slot for those who *don't* speak English. But once you
get past that fact, the choice of another language depends on the
individual's circumstances -- on whether the individual's business
interactions involve speakers of Japanese, Mandarin, German, French, Hindi,
or something else.

If I myself were trying to work out a language learning plan and had no
information about my future business career to help me, I'd first learn
French or German or Spanish -- because they are so much like English, and
would strengthen my language learning skills without undue effort -- and
then I'd move on to Japanese or Mandarin or some other language from a
family unrelated to English. However, that's just "hypotheticalizing"; it
might be useless in your particular circumstances.

In today's global society, what matters is perhaps not so much which
foreign language people learn but that they learn *some* foreign language." 
(SOURCE: Re: What's the best language to learn?
<http://www.linguistlist.org/~ask-ling/archive-1999.1/msg00192.html>).

A "study also showed that nearly a third (29.1 percent) of people 
surveyed felt that knowing French would help or would have helped 
their career or business prospects. 18.1 percent of respondents said
German would be helpful, and 10 percent said Spanish would be the 
best language to learn. Welsh was seventh on the list of useful 
languages, ahead of Chinese and Russian. Only 37 percent said a 
language would not have helped them in their business or working 
life." (SOURCE: GENDER GAP OPENS UP ON LANGUAGE SKILLS, <
http://213.38.88.195/coi/coipress.nsf/0/85201a4f3ed43a7d80256a3b002d41d5?OpenDocument>).

Finally, my own opinion. I vote for German (similar to English),
Mandarin (most widely spoken), or French (still a second language in
many international settings).

Search terms
------------
eu "official languages"
g8 members 
similar  roots  languages  

I hope this answered your question. Please contact me if you need any
clarification before you rate this answer.

Thanks to both politicalguru and czh -- the links in both responses
have proven very helpful. I'm especially liking the concept of "Gross
Language Product". Appreciated.

Hello rwmccauley-ga,,

As you indicated in your question, there are many criteria by which
you can evaluate what languages to study. Many newspapers recently
recapped an article from the journal Science that addressed the future
of global languages. These articles suggest that English as a global
language is in decline. It is now ranked at number two behind Mandarin
Chinese and is followed by Spanish, Hindi/Urdu and Arabic. The
articles also review the trend toward greater bilingualism. Here are
some resources that might be of interest.

http://www.eurekalert.org/kidsnews/index.php?page=graddol-kids
What Languages Will the World Speak in 50 Years?

http://news.nationalgeographic.com/news/2004/02/0226_040226_language.html
English in Decline as a First Language, Study Says

http://www.sciencemag.org/content/vol303/issue5662/sindex.shtml
The Future of Language
David Graddol
Science Feb 27 2004: 1329-1331.
***** You have to be a member/subscriber to be able to access the articles.

http://www.globaled.org/issues/178F.pdf
Language and Society
***** This is a 24-page paper that has several charts ranking
languages by various criteria.

http://esperantic.org/esf/es11.htm
Crystal's Ball and the Ecology of English: An Essay Review
***** This article provides a review of David Crystal?s English as a
Global Language and David Graddol?s The Future of English?

Good luck with your explorations.

~ czh ~

This is an fascinating question and the responses are great. However,
the implication that English is declining as a world language, because
the number of people who speak it as a first language is declining, is
faulty. The real question is how many people speak English fluently or
moderately well (well enough to communicate), and that number is
considerably larger than 322 million (the website listed below claims
that another 400 million people speak English as a second language).
In fact, I recently saw an article (I think from the Economist, but I
couldn't find it quickly) which claimed that English is the first
language in the history of mankind that is spoken by a greater number
of people as a second language than as a first language! Given that
very few people speak Mandarin outside of China (does anyone have a
reliable figure?), the likelihood of Mandarin replacing English seems
rather remote.

( http://iteslj.org/Articles/Kitao-WhyTeach.html )

This website also makes this important comment: "However, even these
numbers do not really indicate how important English is as a world
language, because less than fifteen percent of the world population
uses English. The importance of English is not just in how many people
speak it but in what it is used for. English is the major language of
news and information in the world. It is the language of business and
government even in some countries where it is a minority language. It
is the language of maritime communication and international air
traffic control, and it is used even for internal air traffic control
in countries where it is not a native language. American popular
culture--primarily movies and music--carries the English language
throughout the world."

The article in the Economist below says this: "IT IS everywhere. Some
380m people speak it as their first language and perhaps two-thirds as
many again as their second. A billion are learning it, about a third
of the world's population are in some sense exposed to it and by 2050,
it is predicted, half the world will be more or less proficient in
it."

( http://www.economist.com/world/europe/displayStory.cfm?Story_ID=883997 )