There are tons of programs based on similar ideas and, although, I am not very familiar with it, I am sure there is a lot of research on their effectiveness. But the assumption implicit in your question that unemployment (long-term or not) results from a lack of life-long education that is itself largely voluntary is patronizing and unrealistic.
Also, the people furthest from the regular job market often have to deal with many other issues (ranging from no car/limited mobility, children to take care of – Germany has long been particularly bad in this respect, patchy work history, lack of basic reading or computer skills and difficulties with the local language to lack of basic discipline, addictions, disabilities, psychiatric issues, abusive relationships, etc.) so simply forcing everybody who is unemployed into some sit-down training is unlikely to achieve anything.
Many (intelligent and able) people also have difficulties with the sort of arbitrary discipline and abstract thinking our education system demands to begin with. Often, they disliked school and end up among the least employable precisely because they didn't get any advanced diploma. Bringing them back in the type of school-like environment implied by your suggestions does not sound like a particularly promising idea.
Just to give you an example of what I mean here, I can describe one specific approach I am a little familiar with. In France, there are a number of structures (called “atelier chantier d'insertion”) where long-term unemployed people selected by the national job agency get a one or two-year contract doing things like ironing or growing vegetables (the products/services are sold on the market but the activity would not be profitable without subsidies). For the workers, it means a better income and the possibility to plan ahead a little, an opportunity to show they can hold a job and to (re)learn many basic skills (from coming on time to using a computer) and possibly some more specific marketable skills like working in a retail shop, without being in a school-like environment. The staff typically includes a social worker that should help them prepare a project for the time after the temporary contract.
That's but one specific example but this type of things (and also all sorts of more traditional training) are widespread. But the simple truth is that economic growth makes a huge difference. When the economy is not doing well, qualified applicants are forced to consider entry-level jobs, employers can be picky and less qualified applicants get pushed out. Even the best training won't make someone more attractive than another candidate who just left the exact same job elsewhere.
The fact that periods of high unemployment have long-lasting effects is also well documented. People often slide into long-term unemployment and thus become less and less employable because the less attractive/less stable entry-level jobs they could usually pretend to get filled with other applicants. After struggling to find a job for years, many will understandably retract from the job market entirely and stop being counted as unemployed, sometimes turning to disability payments or other sources of income when available.
In the meantime, at the other end of the job market, employers complain about the lack of skilled workers but that's mostly because they want cheap qualified employees that are immediately effective with the technology du jour, without any effort to recruit or train other potentially qualified applicants. For if there was a genuine shortage of skilled work, in a market-based economy, the logical consequences would be a general wage increase but that has not been happening.
Those (and the catastrophic macroeconomic policies in the EU/Eurozone) are the issues we are dealing with. All the talk about a purported “skill gap” and “training” as a cure for unemployment has been going on for decades but it's a cop out, a way to keep talking about some relatively painless solution (who can oppose education?) without confronting difficult problems.
Incidentally, in Western European countries, there are also opportunities for people who do not speak the language well, some employers even cynically prefer such employees (say for fruit picking, hotel cleaning, etc.) so while learning the local language can benefit anyone, that's not an explanation for long-term unemployment either.
