Syncronize between PC & USB

All Applications from this site are designed to work with changing drive letters.

I don't know the exact Apps but I think that some only adjust the drive letter. That means if you change other parts of the path it might not work. Maybe thats the reason for your error with the german dictionary.

I don't know if there is a "safe" way to change the whole path. But maybe someone else does...

I'm not clear what the problem is. Perhaps you could let us know the exact error message or symptom that you see? At what point does the incompatibility become apparent, and how does it make itself known to you? (Some around here understand German as well as Geek, so most any message can be deciphered.)

As Simeon mentioned, it might be the path changes that are the problem, rather than drive letter. Are you copying it to approximately the same position in the directory, e.g. x:\PortableApps\ThunderbirdPortable, or at some other depth? If you copy to the exact same directory structure (as a test), does the problem go away?

If the message is referring to version, is it possible that it is finding a different copy of the German dictionary (e.g. is there a version of Thunderbird installed, perhaps in the default non-portable location, that might have the incompatible version of the dictionary)?

It may be that you have encountered a bug that can be easily fixed, but I'm guessing we would need more information to be able to replicate the problem.

Edit: I notice that if one installs the dictionary as an add-on, it gets put into ThunderbirdPortable\Data\profile\extensions, instead of ThunderbirdPortable\App\thunderbird\dictionaries as one might expect. I found that if it is in the Data\profile\extensions location, it is ignored when the application directory structure is moved to another location, whereas if it is in the App\thunderbird\dictionaries folder, its usage is maintained. Could this be the problem you are describing?