Hi,

the language pack you are referring to in in jessie-security. There
seems to be a problem with the old amprolla at
auto.mirror.devuan.org:

    $ apt-cache policy thunderbird
    thunderbird:
      Installed: (none)
      Candidate: 1:52.4.0-1~deb8u1
      Version table:
         1:52.4.0-1~deb8u1 0
            500 http://auto.mirror.devuan.org/merged/ jessie-security/main i386 Packages
         1:45.8.0-3~deb8u1 0
            500 http://auto.mirror.devuan.org/merged/ jessie/main i386 Packages
    
    $ apt-cache policy thunderbird-l10n-de
    thunderbird-l10n-de:
      Installed: (none)
      Candidate: 1:45.8.0-3~deb8u1
      Version table:
         1:45.8.0-3~deb8u1 0
            500 http://auto.mirror.devuan.org/merged/ jessie/main i386 Packages
            500 http://auto.mirror.devuan.org/merged/ jessie-security/main i386 Packages
    			   

All is fine instead if you use the new amprolla repo at
pkgmaster.devuan.org:

    $ apt-cache policy thunderbird
    thunderbird:
      Installed: (none)
      Candidate: 1:52.4.0-1~deb8u1
      Version table:
         1:52.4.0-1~deb8u1 0
            500 https://pkgmaster.devuan.org/merged/ jessie-security/main i386 Packages
         1:45.8.0-3~deb8u1 0
            500 https://pkgmaster.devuan.org/merged/ jessie/main i386 Packages
    				
    
    $ apt-cache policy thunderbird-l10n-de
    thunderbird-l10n-de:
      Installed: (none)
      Candidate: 1:52.4.0-1~deb8u1
      Version table:
         1:52.4.0-1~deb8u1 0
            500 https://pkgmaster.devuan.org/merged/ jessie-security/main i386 Packages
         1:45.8.0-3~deb8u1 0
            500 https://pkgmaster.devuan.org/merged/ jessie/main i386 Packages
    				
We must investigate this, but since the old amprolla is due to be
decommissioned (sooner or later), I would probably suggest to switch
your repos to pkgmaster.devuan.org. 

My2Cents

KatolaZ