1. Download the digikam 3.4.0 windows installer which contains the translation.
2. Open it in an archive manager
3. Extract folder $_OUTDIR/locale/de
4. Copy it into C:\Program files\digikam\share\locale\
5. You should now have C:\Program files\digikam\share\locale\de\LC_MESSAGES\digikam.mo
6. Start digikam
7. Menu Help -> Switch application language -> German
8. Restart digikam