For first languages I stick to Ethnologue.com, modified by own materials.

https://www.ethnologue.com/

Under https://www.ethnologue.com/language-development there are criteria lists and some discussion. It is at least sensible to be familiar with this website.

I consider  that the most important methodology is the one that is suitable for the place, I agree that an etnographic study should give you the best answer to find the more appropriate method. In this same site:

https://www.researchgate.net/publication/232825747_English_Language_Teaching_in_Thailand_Today

Article English Language Teaching in Thailand Today

I would suggest simply determining the number of speakers in the community who prefer to use that language, separated into age groups.

I would try to answer your question by looking at language choice between English and other local languages in various domains of language use, e.g., law, education, media, etc. Quantitative method would enable you to see the tendency of language shift and maintenance in a particular society.

In order to determine the future of a language in a specific country, one could try the approach through Linguistic Landscape Studies (LLS). LLS are usually carried out by gathering and analyzing empirical data, by investigating what written language(s) one finds in public spaces. Some interesting studies have been written by Blommaert and Maly on this topic, in a case study titled 'Ethnographic linguistic landscape analysis and social change', (see also https://www.tilburguniversity.edu/upload/6b650494-3bf9-4dd9-904a-5331a0bcf35b_TPCS_100_Blommaert-Maly.pdf).

I am just giving suggestions, I have no experience in this field.  I would go into the community, for example movie theatres, DVD shops, bookshops, TV, magazines, etc.  How important is English to the people?  How about the schools, children?  Are they speaking English informally, reading English stories, watching children's international shows?  Library?  If the children speak or admire English culture, English would be around for some time.........  

I agree with Corine Klip. I plan to add linguistic landscape in my project, too. I also like Belinda Engelmohr's idea. Thanks for posting the question and all the thoughtful answers.

Linguistis are usually accustomed to study the past (= history) of languages, not the future of languages, because nobody has invented a device to travel into the future, bar SF novels, where time machines may be imagined. Therefore we may guess the future of a language based on similar situations in the past. Language is closely connected to ethnicity and/or national identity, at various levels and various intensities. Nobody can guess the future of anything:a big company may become bankrupt over night in case of mismanagement or bad luck or being destroyed by competitors. A language is spoken by people and, therefore, it is connected to the ability of those people to speak it across generations. Note that languages change in time, contemporary English would be probably difficult to be understood by Shakespeare and definitely a foreign language to Chaucer. 

Even the future might not be always predictable, you can always make hypotesis for future scenarios based on the data you can collect now. As example, you can predict that with less than 10 native speakers (all elderly), Saaroa language of Taiwan will be soon exctinct.

I don't know about English in Thailand, but through a internet based questionnaire, I could collect enough data to make good hypotesis on which would be the future of local languages, Chinese and English in Taiwan.

Indeed as professor Paliga said, things can change quite fast, so you must work on hypotesis.

However, you can try to understand which aspects of the society are more influenced by a language and the reason that push people in use/study a language over another. As instance, the reason why minnan language in Taiwan will probably become a minor language of the island, is the fact that do not offer any economic advantage. In Taiwan, children (even 3/4 yo) are regularly sent to English cramschool, with the purpose of make them take advantages in future career. Local langugages (or dialects if you want) are not passed from parents to children for the only reason that do not bring any economic advantage. This fact, with the stereotyped vision that many Taiwanese young people have of "western countries" makes them consider necessary to study English. The future will be a diglossy situation of Chinese and English.

In my opinion, try to investigate what is the daily use of languages, asking people why they choose to speak/study those languages inside and outside family, and understand what the languages you want to investigate means for them (cultural heritage, hobby, economy,etc.), will allow you to start to analyze different future scenarios of a language. I think a well structured questionnaire represent a easy and good way to gather quantitative and qualitative data that you can integrate with other sources.

As last thing, I would like to suggest you to take in consideration also languages that are not your focus, but are spoken in the area you want to analyze. If you want to know what is the future of English in Thailand, you must also take in consideration what could be the future of the other languages that are spoken in Thailand.

As a basic beginning, the vivacity of a language is given by: 1. the demographic aspect: languages with few speakers are prone to extinction within several generations; 2. ethos of speakers: are they desirous to speak a given language?; 3. education: a written language, with a long tradition is expected to have a longer life than a language without a written tradition; 4. various other variable details, e.g. natural growth of population, emigration ~ immigration in a given linguistic area etc. etc.

The most objective measure would be: is the number of speakers of a particular language  increasing (according to census report)?  

Dear all, 

Hello again, 

I really thank you very much for all the thoughtfully thoughtful thoughts you have provided here. I got much from the comments you have provided indeed. I now have a better image of the research I am going to do. Once again, I appreciate the time you have taken to share your views. 

Kind regards, 

Karwan

If I were you, I would stick to an ethnographic-qualitative research methodology where one can use a variety of methods and tools for data collection:

-Semi-structured interviews

-Focus groups

-Documentary analysis

-Think-aloud protocols

Good luck!

Adding to what has already been said, the fact that you are focusing on English is a good starting point for you. I am sure you can find existing research in other countries on the increasing role/importance of English (if that is indeed your focus).

Depending on your background or desired focus, your research could fit into any number of disciplines/sub-disciplines, such as language policy, English as a global language, language acquisition, language maintenance, language ideology, multilingualism etc. Depending on your starting point, the particular methods and research questions you adopt may be quite diverse!

Dear Karan, you may as well use Bourhis, Giles and Rosenthal (1981) Subjective Ethnolinguistic Vitality Questionnaire (SEVQ)  which is based on Giles, Bourhis and Taylor’s (1977) construct of objective ethnolinguistic vitality of languages..

Dear Dr. Mahmoud Abdallah, 

Hello, 

Firstly, I thank you very much for the thoughtful comment. That is actually new for me, I appreciate that indeed. I am just wondering if you could clarify more about those. More specifically, do you know any specific instrument of those tools to be used for collecting necessary data to determine the future of a specific language in a country? Do you believe using more than one of those is necessary to attain the desired data?

Once again, I thank you very much. 

I look forward to hearing from you again. 

Cordially, 

Karwan

Dear Laura Smith-Khan, 

Hello, 

Thank you very much for your view on the question. I am actually interested in determining the future of English language in my country where English is spoken as a foreign language. I am now looking for the necessary instrument and methodology to be utilized to collect the desired data. 

Kind regards, 

Karwan

Dear Prof. Bachir Bouhania, 

Hello, 

I thank you very much for helping and sharing about SEVQ. Indeed, that was new for me. I do appreciate that! 

Regards, 

Karwan

In addition to all the insights already suggested, the government's language policy should be taken into account.

Dear Mrs Omoloso, i totally agree with youas far as the governmental support is concerned yet I also emphasise that the speakers/users of the languages(s) have a very important role to play in the maintenance, shift,  development and/or disappearnce of language.

Professor Omoloso's point regarding the government's language policy is certainly important, since this determines educational requirements. Many variables affect the future of languages in a country. A foreign language may be required in school, but unless it becomes widely used in informal contexts, this will have little effect. In the U.S., not only is Spanish taken in school by a large percentage of children (and in college as well), and spoken by millions of immigrants and their descendants, it is declining in use as measured by the U.S. Census across generations in immigrant families, and is not used in daily life by the millions of native English speakers who have studied it in school. So one can say that Spanish will survive in enclaves as long as the immigrant stream is replenished, but if this is not continued, it will gradually disappear. Huge numbers of Italian speakers immigrated to the U.S. in the 19th century, but Italian is hardly found in the U.S. today outside a few urban centers such as New York City. 

    A simple survey instrument inquiring whether English is spoken by respondents, and with whom and in what contexts, should give a reading of the state of the language in Thailand, or any similar situation. A useful proxy is to determine the circulation numbers of periodicals published in the country, and hours spent watching English-language TV programming. It is essential to include in any survey instrument the age, income level, type of employment, and educational level of the respondent. Languages spoken widely by social elites can disappear overnight, as happened to French in the Russian Revolution, and languages imposed by official policy, such as Russian in East European countries following the end of the Soviet Union, and as such are a cautionary tale for any certitude in predicting the future. 

   --Rudy Troike

     University of Arizona, USA

I agree with the point on usage, also consider if the language is effectively developed (as it will be required for material development et al)

Consider national unity (enhances or otherwise), language of catchment area

Very good contribution, Rudy. I am continually correcting people who believe the US is a bilingual country (English/Spanish) or is likely to be within this century.  As your observations indicate,  if Spanish was not being 'fuelled' by continuing immigration, both legal and illegal, it would suffer the same fate as befell German , Italian, Swedish in the past in the US.

On a different point, I am surprised no one has mentioned demographics.  I grew up in an Ireland in which Irish was the second most widely spoken language, though a long way behind English.  Now, because of the vast and uncontrolled immigration into Ireland of the past fifteen years or so, it is doubtful that Irish would even be listed among the top ten most commonly spoken languages.  Mass Immigration didn't kill the language--it has been in decline for centuries--but I do believe it has accelerated that death by a generation.

Mr Troike

I agree with you in the use of a foreign language. As Puerto Rican, English is taught in the schools as a class from first grade to twelve and then you have to take it in college also at least two more courses. In our daily social life, we use Spanish. At work in some instances, you are in required to interact using the English language but mostly when you are dealing with foreigners such as with big corporation executives or tourists. Unless you had had the chance to study abroad, you are still very hesitant to communicate in English. 

Mr. Mustafa,  in my opinion, the future of English in Thailand will be determined in part by how widely used is the English language in informal context such as part of their daily life. 

take a look at the EGIDS scale, developed by SIL. https://www.ethnologue.com/about/language-status

I was very interested in Dora Alvarez' insider comments on English in Puerto Rico. It was my impression when I visited Puerto Rico a few years ago that English forms only a thin veneer in Puerto Rican society, superimposed by government and external business policy, but Spanish is the true functional language for most daily life. Thanks for corroborating this. 

  I think the appropriate label for such status of a foreign language in a country is "auxiliary language". Given the right circumstances, the external language may replace the native language, but this usually involves conquest (as happened in the Roman invasion of Iberia, or the British occupation of Australia) coupled with great cultural disparity and absence of a strong uniform native language.

   Rudy Troike

Dear colleague,

   The following paper discusses the future of languages in a particular country. It can be useful for you:

  https://www.researchgate.net/publication/286449305_LANGUAGES_TODAY_-_COMPETITION_OF_REGIONAL_NATIONAL_AND_INTERNATIONAL_LANGUAGES_ON_THE_EXAMPLE_OF_GEORGIA

Kind regards,

Article LANGUAGES TODAY – COMPETITION OF REGIONAL, NATIONAL AND INTE...

Dear all, 

Greetings, 

I truly thank you very much for all the insightful and valuable comments you have provided here. They are truly helpful in my project. Once again, I do appreciate you all for taking the time to add your views on the question. Wish you any best! 

Kind regards,  

Karwan