domains / subdomains to subdirectories transition examples

Hi all
i got a multilingual website , where our local content is on separate domains, sometimes subdomains.
we want to transfer those to subdirectories, so in the end of the day out of sample.de we have sample.com/de

before however IT guys demand some proof that this will work.
i can pull myself the success data, but need sample domains
do you know of any domain that did that in recent years ?

I would appreciate sharing !

Simple 301 redirects for permanent or 302 for temp. Not hard at all to do, can't think of an example site but it's all over the web, not a difficult thing to do
moz(dot)com / learn / seo / redirection

You don't need proof, a 301 redirect has been well documented to handle this change without issues.