Between Integration and Return:
The Reality of New Syrian Refugees
A Survey of Refugees in Germany,
France, the Netherlands, and Sweden This, 2021, long, report gives some indication about specifically the Syrian refugees. This seems self-reported, rather than test-assessed.
The percentage of those defining their level of host-country language proficiency as “good” or “very good” was largest
among those in the 18-25 age group. According to the survey, 61.2% of respondents aged 18-25 said their language level
is “good” or “very good,” while 43.6% of respondents aged 26-39 rated their language proficiency level as “good” or “very
good.” Among those 40-55 years, this percentage dropped to 20%. A clear difference can be seen between the average
within the younger age group and the overall average of respondents who said their level of language proficiency is “good”
or “very good,” which was about 37%.
This apparent relation between age and language proficiency level is linked to several factors, including the faster learning
process for younger people and the involvement of a large number of younger people, especially those 18-25 years, in the
educational process that helps raise host-country language proficiency levels.
Seems like a clear could do better. Either for the immigrants or the host country. I found it by way of Europe’s mounting challenge to integrate Syrian refugees @ TRTWorld which went on to say Sweden had the worst rate of the 4 countries, something I found surprising.
Overall, seems like a really in depth survey, also covering other subjects like social liberalism or employment rates.
Otherwise, this subject seems sparsely covered. For example, I found a Netherland report that refers to a survey. Said survey data is said to be unavailable to the general public, but links to summaries are provided. Links which then 404 in English, and lead to long lists of not-all-relevant documents in Dutch.
p.s. adding a comment I made about the criteria cited in the Q:
using the C1 level seems unduly demanding - Can use language flexibly and effectively for social, academic and professional purposes./Can produce clear, well-structured, detailed text on complex subjects - seems to be a high bar for even natives of a country. Not because they can't, because their day-to-day life and job does not require it.
Plus, from personal experience, 600 to 1200 hours of class time does not result in C2 - top level - proficiency in a language. Not even close, so the effort required seems very underestimated.