Just a little remark to the German sentences:
"Dein" is second person singular, which means a rather close relationship between the two parties.
Better (as I think) it would be to make use of a more old-fashioned way of adressing the player by using "Ihr/Euer/Eure..."
[edit] This means second person plural and is a more reserved way to adress the other one, which I think would fit better into the diplomatic context. [/edit]
In addition I have a different proposal for the TXT_KEY_MISC_ATTITUDE_LOST_WAR.
I have taken the liberty to transfer it according to my proposal like follows (changes in bold letters):
Last and important too, the German language has quite some letters which are not in the latin set of letters, as 'ä', 'ö', 'ü' (and the capital letters of them).
As far as I remember, those letters would have been to replaced by certain codes to work correctly.
If you think my comments might be helpful, I could try to find out about such codes and update my proposal.