Launcher:

Karte Editor --> Karteneditor

Andere möglichkeiten --> Weitere Optionen

Videospieler --> Translation is correct, though it sounds strange. Still 
thinking about a better word. Maybe "Video Player"

Main menu:

Single Player: "Einzelspieler" or the english word "Singleplayer"

Multiplayer: "Mehrspieler" or the englisch word "Multiplayer"

Intro: "Einleitung" is ok...."Intro" works as well

I'm now looking at the translations ingame.

Why did you do a new tranlsation? It sounds like an automated translation now 
for some of the words and sentences. The german translation from the Dos 
version was just fine.

Main menu:

Video --> "Videos" or "Filmarchiv" (means movie archive and is used sometimes 
in german translations)

Only certain things were available in german: database text, building and 
technology descriptions, battle finish texts. Everything else had to be 
created. My german is a little bit old and non-technical, this is why I used a 
translator. 

Well, you could have checked the german version. I know someone who owns the 
images ;)

Just kidding. I'll do it. Will take some time though.

[deleted comment]

so all the other stuff was hardcoded into the exe?

Btw.: I'm actually studying german...so i hope that helps :)

The chat is in TEXT.PAC as well, but the new Objectives panel and all the 
mission text never ever appeared in the original. I had to "invent" them, and I 
didn't bother with the notification texts in any language.

Take your time. (The next major step will be the implementation of space-chat.)

other options:

release notes --> "Versionshinweise" 

Project webpage --> "Projekt Webseite", just a typo

run settings --> your translation doesn't make any sense but I guess you mean 
settings regarding the jave runtime environment, I'm pretty sure you mean 
"Laufzeit Einstellungen" though not many german gamer know such technical 
terms. Maybe something like "Start-Einstellungen" (means "start settings") ist 
better.

Verify installation --> Installation überprüfen", just a typo

[deleted comment]

Main menu still has two typos:

EinzelspiEler and MehrspiEler...you forgot the "E"