qgis - Error using grass v.clean: " 'utf-8' codec can't decode byte... "

I try running the v.clean tool using QGIS 3.4. As input I use a vector line layer (I checked the validity and everything is fine), but running the algorithm I get the following error:

Traceback (most recent call last):
File "D:/Programme/OSGeo4W/apps/qgis/./python/plugins\processing\algs\grass7\Grass7Algorithm.py", line 415, in processAlgorithm
Grass7Utils.executeGrass(self.commands, feedback, self.outputCommands)
File "D:/Programme/OSGeo4W/apps/qgis/./python/plugins\processing\algs\grass7\Grass7Utils.py", line 372, in executeGrass
for line in iter(proc.stdout.readline, ''):
File "D:\Programme\OSGeo4W\apps\Python37\lib\codecs.py", line 322, in decode
(result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf6 in position 81: invalid start byte

Execution failed after 0.50 seconds

Since it is says it is a decoding error I checked the encoding and it is encoded in UTF-8.

Does anybody know how to solve the error?

Answer

QGIS version 3.4.2:

The bug is fixed in version 3.4.2 and everything works without error messages.

Note: This only works since QGIS version 3.4.2, if you use a previous version of 3.x please update QGIS or check a possible workaround I mentioned below.

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Below 3.4.2:

In versions 3.x the error is a known QGIS bug and is triggered by regional language settings on Windows.

A current workaround is to switch the Windows system language to English (US) and the error will disappear.