Patch for German Version from 1.00 t0 1.58?

There is no 1.58 patch for the german/international version yet.

Every patch contains all fixes, so you can install the 1.58 patch on version 1.00 and it will work.

You could install the english version and then the 1.58 patch - this should work. (Or it was 1.00 -> 1.44 international -> 1.58)

Alliance functions have been added, but i don't think they are used in the scripts yet.

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In the international package distributed in Europe by Empire Interactive there are bundled together several local language versions of SE5, English (not to be confused with American!), German, French etc. Version numbers differed, German was 1.33, English 1.30, etc. The international patch 1.44 fixed all the versions of the package to 1.44, in the respective language. So far so good.
Now 1.58 turned out to be compliant with the English 1.44 of SE5, but, as far as I know, not with the others - I have no idea if or when Empire Interactive will issue 1.58 for the other language versions of SE5.
If you have the international package and want to play 1.58, you have to install the English version (1.30) of the package, then the international 1.44 patch, and finally the standard (U.S.) patch 1.58.

Blackguard, you do have the English version! When you installed the game, you were asked to choose an installation language, remember? You chose German, didn't you? Had you selected English, the English version would have been installed.
You can un-install the German version and re-install the English one. I don't know what happens to save games, but my guess would be that they are not compatible (you can create a copy of the German version before you un-install it - maybe it will continue to work after re-installing the English version, but I haven't tried it).
Here is where you can get the European 1.44 patch: http://support.empireinteractive.com/default.aspx?MID=60568495217F&PID=78433F16-528C-4432-8252-7862947EB934 (or go to www.empireinteractive.com, search for the SE5 page and click on Downloads).
This patch will update both versions, but you can apply the 1.58 patch to the English 1.44 only, sorry, so you better install the English version of the European SE5 package.

I don't think your save games are gone. You may not be able to open them, but I'm sure they are still there (if you did nothing but apply the patch). Sometimes patches are not save-game-compatible, 1.44 may be one of them - wouldn't be a surprise, given that SE5 is still a "living" game.
If you want to convince yourself, simply have a look at the "savegame" folder within your SE5 installation folder.
And if you want to continue playing your old save games, you may un-install SE5 (back up your savegame folder first) and re-install the German version 1.33 (without applying the patch). Then you can copy the backed up savegame folder back to the SE5 folder and continue playing your old games (but possibla not the new ones you started based on 1.44)!