This is how I understand the options of units.xml so far:

- units can have multiple representations per language, example is "deg" and "°" for degrees (angular units). If you use them in english unit language setting, then they are saved correctly.

- If you define alternative german representations like "°" and "Grad", then always the same english version is saved, such that upon loading the document, you have all one unit (the first definition for the current language setting in. Thus, whenever you want to save different versions of a unit, then they need to belong to different english versions.

- You can define units without providing english versions. Example: "Morgen". They are then saved in the german version or whatever is available.

- You cannot have different units with the same english name, but you can have different english names for the same unit. This is sort of advantage for english, as the use of different english versions of the same unit survives save/reload, whereas for other languages they do not.

- It might be possible to re-define the base units. I am not going to try that, because I am happy with the metric system and messing around without solid knowledge of the internal logic is a nightmare of trial and error.

In order to get more insight and make modifications more robust, as many as possible people should try the modified units.xml posted above.
This shall become part of the inofficial distribution with the next release.

First I had the idea to just change the 15th mantissa position of the value attribute, but then thougth that this dirty engineering approach (minimal effort, no loss of features) would not be overly welcome by the math community.

Thus I sacrified multiple german unit names for the sake of acceptance in the distribution.