chore(de-translations): Add and fix German translations

[hbruch]

SUMMARY

This PR adds missing and improves some German translations, based on current POT file.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

1. Enable German translations by adding "de": {"flag": "de", "name": "Deutsch"}, to the enabled LANGUAGES (I'd eve suggest to add this now per default, as it should be fully translated)
2. start superset
3. Switch to German translations and check, if all messages are translated and meaningful

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #17631 (fad86f4) into master (a3cce57) will decrease coverage by 0.18%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #17631      +/-   ##
==========================================
- Coverage   68.57%   68.39%   -0.19%     
==========================================
  Files        1602     1602              
  Lines       65349    65349              
  Branches     6992     6992              
==========================================
- Hits        44816    44695     -121     
- Misses      18647    18768     +121     
  Partials     1886     1886              

Flag	Coverage Δ
hive	?
mysql	81.80% <ø> (ø)
postgres	81.81% <ø> (ø)
presto	?
python	81.89% <ø> (-0.41%)	⬇️
sqlite	81.49% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/db_engines/hive.py	0.00% <0.00%> (-85.19%)	⬇️
superset/db_engine_specs/hive.py	70.27% <0.00%> (-16.99%)	⬇️
superset/db_engine_specs/presto.py	83.50% <0.00%> (-6.89%)	⬇️
superset/views/database/mixins.py	81.03% <0.00%> (-1.73%)	⬇️
superset/connectors/sqla/models.py	86.85% <0.00%> (-1.58%)	⬇️
superset/models/core.py	89.26% <0.00%> (-0.74%)	⬇️
superset/db_engine_specs/base.py	88.15% <0.00%> (-0.39%)	⬇️
superset/utils/core.py	89.64% <0.00%> (-0.12%)	⬇️

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[hbruch]

@villebro the failing test again seems to be a flaky test, or is there anything I can do about it?

[villebro]

Thanks again @hbruch - I restarted CI and will babysit until it passes

[villebro]

LGTM!

[villebro]

Vielen dank @hbruch !