Watched Breaking the language barrier | Tim Doner | TEDxTeen 2014 from YouTube

Tim Doner is a senior at the Dalton School in New York City who has studied over 20 languages. His interest started at the age of 13, after several years of French and Latin, when he began learning Hebrew and soon moved on to more obscure tongues such as Pashto, Ojibwe and Swahili. As he describes it, his goal is not to achieve fluency in each, but rather to learn about foreign history and culture through the medium of language. He spends much of his time perfecting his linguistic skills in different neighborhoods around the city, and to date his Youtube channel has received over 3 million hits. Tim has been interviewed (in English, Mandarin, Arabic and Farsi, among others) for media outlets such as The New York Times, BBC, The Today Show, Reuters and The Economist. He is starting his freshman year at Harvard next year and plans to study linguistics.

A nice hook to pull one into some of the reasons why one would want to pick up languages as well as how to do so.

8:44 method of loci (locorum)

10:02 Learning words in groups based on related sounds.

11:22 Why learn languages? Some useful motivation here.

Language represents a world cultural view. This is particularly poignant because a language (and its methods of thinking, viewing the world, and usually lots of associated culture) disappears from the world every two weeks.

Read Merriam-Webster changes its definition of 'sexual preference' as Barrett gets called out for using term (Fox News)
Merriam-Webster dictionary changed its definition of “sexual preference” to include the word “offensive” as Democrats slammed Supreme Court nominee Judge Amy Coney Barrett for using the term during Tuesday’s Senate confirmation hearings.
Interesting to see historical linguistics playing out in real time in the news apparently.
Read What's Next? Scots, Scottish Gaelic, and the Scottish Identity by Melissa Puthenmadom (eucenterillinois-language.blogspot.com)
With the Scottish independence referendum looming over the horizon—scheduled to take place on September 18, 2014—the presence of Scotland’s regional and minority languages has become more relevant than ever. Today, the only official language in Scotland is English, while Scottish Gaelic and Scots are recognized as regional languages. You might ask: what’s the difference?
Read Language in England and Wales - Office for National Statistics (ons.gov.uk)
Using data from the 2011 Census, we take a closer look at language within England and Wales. Those who reported English (or Welsh in Wales) as their main language accounted for 92.3% of the population, except in London where proportion was much lower. Those who reported another main language accounted for 7.7% of the population, with Polish topping the list of "other" main languages. London and the West Midlands saw the highest percentage of people who could not speak English "well" or "at all".
Read Most Spoken Languages (most-spoken-languages.sanstream.nl | SanStream Studio)
When we are young we first learn the language from the people around us. This helps us to communicate, share ideas and learn from them. Most of the time just this is just one, but it can be more than one. The last decades the network of people that human being know (due to globalisation) has shifted from knowing just the people in your local area to people all across the world. In order to effectively communicate with other people from across the world it is useful to speak a shared language.

Finding data 

You’re right about data here. I follow some research out of the MIT Media lab by Cesar Hidalgo who may have some interesting data resources if you poke around.

Some additional starting points:

Read UK accused of failing to promote minority languages by Severin Carrell (the Guardian)
Critical report by Council of Europe calls for more support for Cornish, Irish and Ulster Scots
The benefits of speaking multiple languages are fairly well documented. How can we–as a society–better support additional languages? Why are we constantly sidelining and devaluing people’s mother tongues? 
Watched How to learn any language in six months by Chris Lonsdale from TEDxLingnanUniversity | YouTube
Chris Lonsdale is Managing Director of Chris Lonsdale & Associates, a company established to catalyse breakthrough performance for individuals and senior teams. In addition, he has also developed a unique and integrated approach to learning that gives people the means to acquire language or complex technical knowledge in short periods of time.
Attention, meaning, relevance and memory

Five Principles

  1. Focus on language content that is relevant to you (We learn tools fastest when they are relevant to us)
  2. Use your language as a tool to communicate from day 1
  3. When you first understand the message you will unconsciously acquire the language (Krashen ,2013)
  4. physiological training
  5. Psycho-physiological state matters, learn when happy and don’t get frustrated

7 actions for rapid language acquisition

  1.  Listen a lot (brain soaking)
  2. Focus on getting the meaning first (use body language)
  3. Start mixing and be creative
  4.  focus on the core
    1. Week 1: The Tool box (learn to say the following all in the target language)
      * What is this
      * How do you say?
      * I don’t understand
    2. Week 2-3 pronouns, common adverbs, adjectives
    3. Week 4 glue words, but and, though
  5. Get a language parent to help you understand
    1. works to understand what you are saying
    2. does not correct mistakes
    3. confirms understanding by using correct language
    4. uses words the learner knows
  6. Copy the face
    1. Work on the muscles and look at native speakers
  7. Direct connect to mental image (visual association)
Watched Gaelscoilis -- error-laden pidgin or creative creole by Breandan mac Ardghail from TEDxFulbrightDublin | YouTube
Breandán Mac Ardghail's talk is entitled Gaelscoilis: An error-laden pidgin or a deviously creative creole? By exploring the weird and wonderful linguistic features of the language spoken in Irish immersion schools, he offers an alternative perspective on the non-native schoolyard Irish of Gaelscoil pupils. In 2012, Breandán was a Fulbright Foreign Language Teaching Assistant at the University of Montana.
Watched Deconstructing Myths about the Irish Language by Colm Ó Broin from TEDxBallyroanLibrary | YouTube
Colm Ó Broin is an Irish speaker from Clondalkin, Dublin, and a member of Conradh na Gaeilge. He has been involved with Áras Chrónáin in Clondalkin and Cainteoirí Chill Mhantáin in Wicklow Town organising social events for Irish speakers for several years. He worked as a journalist for the Irish language newspapers Gaelscéal and Lá and has spoken and written widely about the many myths that surround the Irish language, including articles in The Irish Times, The Journal and Broadsheet.ie Colm Ó Broin is an Irish speaker from Clondalkin, Dublin, and a member of Conradh na Gaeilge. He has been involved with Áras Chrónáin in Clondalkin and Cainteoirí Chill Mhantáin in Wicklow Town organising social events for Irish speakers for several years. He worked as a journalist for the Irish language newspapers Gaelscéal and Lá and has spoken and written widely about the many myths that surround the Irish language, including articles in The Irish Times, The Journal and Broadsheet.ie This talk was given at a TEDx event using the TED conference format but independently organized by a local community. Learn more at https://www.ted.com/tedx
Watched The Irish Language and Beauty by Dónall Ó Héalaí from TEDxBerkeley | YouTube
Language represents an essential component of humanity, revealing so much about culture, heritage, literature, and nearly every human endeavor. In his TEDxBerkeley 2018 talk titled “The Irish Language and Beauty,” Dónall Ó Héalaí shares his personal relationship with the endangered Gaelic language. Recounting ancient legends, singing a traditional Gaelic song and discussing the colonial induced displacement of indigenous culture and practices, Dónall ultimately encourages the audience to consider our own inner selves--aspects of ourselves that we fail to celebrate and hide from the rest of the world. This talk was given at a TEDx event using the TED conference format but independently organized by a local community. Dónall Ó Héalaí is an Irish actor and the founder of Celtic Consciousness, an initiative that aims to share the insights and beauty of the Gaelic language with a wider audience and use ancient Irish stories and songs as a medium for self-reflection.
Another mention of language connecting it’s speakers to the land here.
Watched Mind yer Scots - Dr Michael Dempster full interview from YouTube
Dr Michael Dempster - Full Interview. Speaking to 'The Big Night In' Dr Dempster discusses the origins of the Scots language, Scots in popular culture, place names, common attitudes and various initiatives to encourage people to use and understand their own Scots tongue.
Interesting note about the TV show Shetland and the language used and how it was affected by the BBC as a production entity.

Mention around 23 minutes about the Anglicization of Scots words that not only don’t make sense, but remove the relationship between the people and their land.

Watched We'r Needin tae Talk Aboot Wir Language by Michael Dempster from TEDxInverness | YouTube

Auditory neuroscientist Michael Dempster delivers a gripping presentation on how the mind reacts when we talk freely with the language we grew up with. This talk is delivered using the language which Miachael grew up with, Scots. He tells of some of the difficulties the Scots language has faced in the past and gives some insight into its future. Michael is an Auditory Neuroscientist who gained his Ph.D. in psychology from the University of Glasgow for his work exploring neural processing fundamental to language and music perception. He is also a first-language Scots speaker. He has taught modern Scots to people from outwith Scotland and to people from Scotland who want to learn more about their own ways of speaking. Over the past year he has been working on his forthcoming book “Mind yer language? - How we talk English an how we talk Scots.”