I ended up living many countries and met many people across the globe and here are my observation on education of a secondary language etc.
Canada: They learn either English or French as a second language. Most of the people however do not speak French unless they live in Quebec, New Brunswick, Nova Scotia, eastern Ontario or a small pocket in Manitoba. They have immersion programs in which they learn many subjects in a second language. Some people speak two languages perfectly, but Québécois are better in language skills since they have more economical insensitive to learn English. Many federal government jobs require the proficiency in two languages. Quebec anglophones derogatorily call a francophone a Pepsi meaning that a francophone can only afford Pepsi since it is cheaper.
USA: Predominantly mono-lingual population, unless they are the first or second generation immigrants. Many educated people do speak a second or third language fluently.
England: The variation of English within England or UK is extremely high. Many people with higher education speak French fluently.
Wells and Ireland: They do learn their own languages in school and many signs are written in two languages. But these are considered to be heritages to be protected not practical tools, it seems.
Scotland: Probably they learn Scottish language in school. Foreigners have hard time to understand English of native Scots. The difference in socio-economic classes seems to be very high. A German who lived in Holland said Glasgow is the closest thing to a developing country which he ever experienced: high poverty rate and dirty streets.
Holland: Many folks speak mostly fluent English since English and Dutch are similar in many aspects. Dutch mostly does not have a strong “g” sound: “g” sounds like that of “enough” and it has a strong “r” sound.
Italy: Most likely, people on the streets in small cities do not understand English. Younger people do speak better English. Most of the movies are dubbed in Italian. People in northern part probably speak better English than those in south. Africans may experience racial bias according to an Italian who lived in USA and studying in UK.
Sweden: My friend who grown up in Florida told me that if he speaks normal American English at full speed they do not understand his English. He had to speak in Swedish-English.
Nepal and India: Educated people speak English but the proportion of educated people is small.
China: Their reading and writing skills are better than their communication skills in general. Japanese can understand Chinese-English but many others tell that they do not understand Chinese-English. Chinese people often told me that natives speak too fast. Many Chinese can speak decent Japanese and can read and they think Japanese is easier than English.
Belgium: Language situation is very complicated in Belgium so let me just oversimplify it. They are bilingual in French and Dutch in theory. In practice and in general, these two groups make fun of each others if not downright rejection so often they communicate each other in English. eg. In a shop in Flanders, they ask to speak in English instead of French. Wallon, many people do not speak other than French. Of course, a lot of people are multi-lingual. Laws in both Flanders and Wallon are preventing English to play bigger roles and many scientists think these regulations are bad for their science. In Flanders, all the official documents must be written in Dutch and often there is no English translation. Also Belgian official documents in English do not often make sense either. (eg, doctors and secretaries in a Boston hospital did not understand sentences.)
Belgian people who never lived in English speaking countries are weak in idioms. They can not figure out probably because the meaning of a combination of words in English is totally different from that of Dutch. And Dutch and German are notorious for constructing big words by adding words infinitely. Also Japanese R and Dutch R are totally incompatible.
People who have a MS/Phd are likely to speak better English since English is often used in master courses. PhD candidates do not take any courses nor teach since they are considered to be employed by Flanders government. To enter a PhD program, a candidate must defend her PhD proposal in front of an external committee for acceptance. The acceptance rate for PhD program is about 1/8, and if she fails to defend her proposal, then she has to wait 2 years for her second try. Probably applying more than one program is not easy or impossible. Once accepted in her PhD program, she can enjoy much more protected status and less competition than in USA or Canada and earn higher pay. Once she must publish 3-4 first author papers. The defence itself seems to be a more ceremonial than actual examination since the thesises are already printed out before the defence. Belgium institutions suffer a lack of man power since the cost of hiring is quite high and working hours are shorter.
Fluctuation of language skill during a week:
A prof who is a French native speaker told that his language skill changes a lot during a week. During weekends, he speak only French and does not speak Dutch at all and English is unthinkable. On Monday, he starts catching up his Dutch but does not want to teach in Dutch on that day. As days go by in the week, his Dutch gets better and he can speak Dutch best in Thursday. In Friday he works at home.
Overall learning English is cheap and easy while it may take long time. For example, learning Dutch is difficult since often there are no good texts, dictionaries nor audio tapes and they are often quite expensive even in Belgium. There are more English learning texts than for Dutch. Also there are very good texts for French and they are cheap. It is difficult to find texts for advanced subject in Dutch as well. So there is little incentive to learn Dutch for scientists. Or probably I just do not know where to find them.
Overall, learning a second language without immediate necessity is difficult particularly if there are more important priorities. People who have enough skills in their profession can get by with their poor oral communication skills as long as they can write.
Many Japanese researchers can communicate well in English and get various many prizes in meetings. But many of friends told me that they often saw many Japanese presenters whose English they could not understand in meetings. But extremely bad presentations are not limited to Japanese.
Probably universally effective learning method for any subjects does not exist. In the end it is up to individuals who must find the way to educate themselves enough to compete in their own field in the world. Individuals should know the best method to educate themselves since they are the only ones who know what need to be done. So my conclusion is a very useless one, indeed, to help others or students.