Do SSL Certs containing two wildcards work (esp. on Let's Encrypt)?

I want to include two wildcards in an SSL cert (will be) signed by Let's Encrypt: *.*.thost3.de. Will this cert match any hostnames matching that rule (e.g. example.example.thost3.de, hello.world.thost3.de), and can Let's Encrypt accept such wildcards exist in certs they signed?

No this SHOULD NOT (in the RFC meaning of "SHOULD NOT") work, as documented in RFC 6125 (Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)):

If a client matches the reference identifier against a presented
identifier whose DNS domain name portion contains the wildcard
character '*', the following rules apply:

1. The client SHOULD NOT attempt to match a presented identifier in which the wildcard character comprises a label other than the left-most label (e.g., do not match bar.*.example.net).

2. If the wildcard character is the only character of the left-most label in the presented identifier, the client SHOULD NOT compare against anything but the left-most label of the reference identifier (e.g., *.example.com would match foo.example.com but not bar.foo.example.com or example.com).

[...]

Putting these two together:

• you can't have a wildcard elsewhere than the leftmost part (separated by a dot) of the certificate: an inner wildcard is invalid.
• you can't have a wildcard certificate match additional label part (ie: separated by a dot) on its left: again that means that if a valid single wildcard were used, nothing with an additional left part can match (so hello.world.thost3.de can't match the certificate *.thost3.de).

What you can do is issue a certificate with a lot of SAN parts possibly themselves with a (valid) wildcard. But I'm not sure at all that you can get this accepted by Let's Encrypt.

EDIT: *.stackexchange.com is signed by Let's Encrypt with multiple SANs having a wildcard.

Example:

$ openssl s_client -connect stackexchange.com:443 </dev/null 2>/dev/null| openssl x509 -noout -text | grep -A1 'X509v3 Subject Alternative Name' | tr ',' '\n'
            X509v3 Subject Alternative Name: 
                DNS:*.askubuntu.com
 DNS:*.blogoverflow.com
 DNS:*.mathoverflow.net
 DNS:*.meta.stackexchange.com
 DNS:*.meta.stackoverflow.com
 DNS:*.serverfault.com
 DNS:*.sstatic.net
 DNS:*.stackexchange.com
 DNS:*.stackoverflow.com
 DNS:*.stackoverflow.email
 DNS:*.superuser.com
 DNS:askubuntu.com
 [...]