Problem with installing Plone 5.2.1 with --build-python=3

I am on Debian 10 as user "plone" and issued the following command from Plone-5.2.1-UnifiedInsaller-r3.tgz.

./install.sh --build-python=3 --target=$HOME/Plone --owner=plone --clients=2

Unfortunately, the build did not succeed. One suspicious part you find below.
Do I have to care about these modules? Note that I put --build-python=3, so why does not the UnifiedInstaller just build the missing parts? Or what else could be missing on my system?

However, it seems the actuall error happens when the sytem tries to apply the Hotfix in 5.2.1, see end of the message. How can I go on?

========================

INFO: Can't locate Tcl/Tk libs and/or headers
warning: building with the bundled copy of libffi is deprecated on this platform.  It will not be distributed with Python 3.7

Python build finished successfully!
The necessary bits to build these optional modules were not found:
_dbm                  _gdbm                 _lzma              
_sqlite3              _tkinter                                 
To find the necessary bits, look in setup.py in detect_modules() for the module's name.

The following modules found by detect_modules() in setup.py, have been
built by the Makefile instead, as configured by the Setup files:
atexit                pwd                   time               

=========================================
The actual error at the end of install.log is this:

Getting distribution for 'Products.PloneHotfix20200121==1.1'.
Got Products.PloneHotfix20200121 1.1.
Getting distribution for 'plone.restapi==6.1.0'.
WARNING: The easy_install command is deprecated and will be removed in a future version.
Traceback (most recent call last):
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 154, in save_modules
    yield saved
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 195, in setup_context
    yield
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 250, in run_setup
    _execfile(setup_script, ns)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 45, in _execfile
    exec(code, globals, locals)
  File "/tmp/plone/easy_install-0zd6kje8/plone.restapi-6.1.0/setup.py", line 14, in 
  File "/home/plone/Plone/zeocluster/lib/python3.6/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2254: ordinal not in range(128)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "", line 1, in 
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/command/easy_install.py", line 2321, in main
    **kw
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/__init__.py", line 145, in setup
    return distutils.core.setup(**attrs)
  File "/home/plone/Plone/Python-3.6/lib/python3.6/distutils/core.py", line 148, in setup
    dist.run_commands()
  File "/home/plone/Plone/Python-3.6/lib/python3.6/distutils/dist.py", line 955, in run_commands
    self.run_command(cmd)
  File "/home/plone/Plone/Python-3.6/lib/python3.6/distutils/dist.py", line 974, in run_command
    cmd_obj.run()
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/command/easy_install.py", line 424, in run
    self.easy_install(spec, not self.no_deps)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/command/easy_install.py", line 666, in easy_install
    return self.install_item(None, spec, tmpdir, deps, True)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/command/easy_install.py", line 711, in install_item
    dists = self.install_eggs(spec, download, tmpdir)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/command/easy_install.py", line 896, in install_eggs
    return self.build_and_install(setup_script, setup_base)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/command/easy_install.py", line 1164, in build_and_install
    self.run_setup(setup_script, setup_base, args)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/command/easy_install.py", line 1150, in run_setup
    run_setup(setup_script, args)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 253, in run_setup
    raise
  File "/home/plone/Plone/Python-3.6/lib/python3.6/contextlib.py", line 99, in __exit__
    self.gen.throw(type, value, traceback)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 195, in setup_context
    yield
  File "/home/plone/Plone/Python-3.6/lib/python3.6/contextlib.py", line 99, in __exit__
    self.gen.throw(type, value, traceback)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 166, in save_modules
    saved_exc.resume()
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 141, in resume
    six.reraise(type, exc, self._tb)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/_vendor/six.py", line 685, in reraise
    raise value.with_traceback(tb)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 154, in save_modules
    yield saved
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 195, in setup_context
    yield
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 250, in run_setup
    _execfile(setup_script, ns)
  File "/zlocal/sdb1/plone/Plone/zeocluster/lib/python3.6/site-packages/setuptools/sandbox.py", line 45, in _execfile
    exec(code, globals, locals)
  File "/tmp/plone/easy_install-0zd6kje8/plone.restapi-6.1.0/setup.py", line 14, in 
  File "/home/plone/Plone/zeocluster/lib/python3.6/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2254: ordinal not in range(128)
An error occurred when trying to install /zlocal/sdb1/plone/Plone/buildout-cache/downloads/dist/plone.restapi-6.1.0.tar.gz. Look above this message for any errors that were output by easy_install.
While:
  Installing client1.
  Getting distribution for 'plone.restapi==6.1.0'.

An internal error occurred due to a bug in either zc.buildout or in a
recipe being used:
Traceback (most recent call last):
  File "/home/plone/Plone/zeocluster/lib/python3.6/site-packages/zc/buildout/buildout.py", line 2174, in main
    getattr(buildout, command)(args)
  File "/home/plone/Plone/zeocluster/lib/python3.6/site-packages/zc/buildout/buildout.py", line 817, in install
    installed_files = self[part]._call(recipe.install)
  File "/home/plone/Plone/zeocluster/lib/python3.6/site-packages/zc/buildout/buildout.py", line 1603, in _call
    return f()
  File "/zlocal/sdb1/plone/Plone/buildout-cache/eggs/plone.recipe.zope2instance-6.5.1-py3.6.egg/plone/recipe/zope2instance/recipe.py", line 146, in install
    installed.extend(self.install_scripts())
  File "/zlocal/sdb1/plone/Plone/buildout-cache/eggs/plone.recipe.zope2instance-6.5.1-py3.6.egg/plone/recipe/zope2instance/recipe.py", line 830, in install_scripts
    requirements, ws = self.egg.working_set(['plone.recipe.zope2instance'])
  File "/zlocal/sdb1/plone/Plone/buildout-cache/eggs/zc.recipe.egg-2.0.7-py3.6.egg/zc/recipe/egg/egg.py", line 87, in working_set
    allow_unknown_extras=bool_option(buildout_section, 'allow-unknown-extras')
  File "/zlocal/sdb1/plone/Plone/buildout-cache/eggs/zc.recipe.egg-2.0.7-py3.6.egg/zc/recipe/egg/egg.py", line 168, in _working_set
    allow_unknown_extras=allow_unknown_extras)
  File "/home/plone/Plone/zeocluster/lib/python3.6/site-packages/zc/buildout/easy_install.py", line 957, in install
    return installer.install(specs, working_set)
  File "/home/plone/Plone/zeocluster/lib/python3.6/site-packages/zc/buildout/easy_install.py", line 730, in install
    for dist in self._get_dist(req, ws):
  File "/home/plone/Plone/zeocluster/lib/python3.6/site-packages/zc/buildout/easy_install.py", line 574, in _get_dist
    dists = [_move_to_eggs_dir_and_compile(dist, self._dest)]
  File "/home/plone/Plone/zeocluster/lib/python3.6/site-packages/zc/buildout/easy_install.py", line 1745, in _move_to_eggs_dir_and_compile
    [tmp_loc] = glob.glob(os.path.join(tmp_dest, '*'))
ValueError: not enough values to unpack (expected 1, got 0)

What is the output of
env|grep LC
?

plone portal10:~>env|grep LC
LC_ADDRESS=en_US.UTF-8
LC_NAME=en_US.UTF-8
LC_MONETARY=en_US.UTF-8
LC_PAPER=en_US.UTF-8
LC_IDENTIFICATION=en_US.UTF-8
LC_TELEPHONE=en_US.UTF-8
LC_MEASUREMENT=en_US.UTF-8
LC_TIME=en_US.UTF-8
LC_NUMERIC=en_US.UTF-8

I assume that

export LC_ALL=C

would solve the issue for the environment where you run or install Plone.

Thanks for the hint. I've put "export LC_...=C" for all the above variable and also export LANG=C into .profile and ran the command again, so after renewed login I now have
$ env |grep LC
LC_ADDRESS=C
LC_NAME=C
LC_MONETARY=C
LC_PAPER=C
LC_IDENTIFICATION=C
LC_TELEPHONE=C
LC_MEASUREMENT=C
LC_TIME=C
LC_ALL=C
LC_NUMERIC=C

Unfortunately, "./install.sh --build-python=3 --target=/home/plone/Plone --clients=2 zeo" gives exactly the same error.