I am trying to export Arabic translation in ODoo 11 EE, but am getting 'AssertionError'

     Error:

Odoo Server Error

Traceback (most recent call last):

  File "/home/shar/Projects/odoo-11E/odoo/http.py", line 650, in _handle_exception

    return super(JsonRequest, self)._handle_exception(exception)

  File "/home/shar/Projects/odoo-11E/odoo/http.py", line 310, in _handle_exception

    raise pycompat.reraise(type(exception), exception, sys.exc_info()[2])

  File "/home/shar/Projects/odoo-11E/odoo/http.py", line 692, in dispatch

    result = self._call_function(**self.params)

  File "/home/shar/Projects/odoo-11E/odoo/http.py", line 342, in _call_function

    return checked_call(self.db, *args, **kwargs)

  File "/home/shar/Projects/odoo-11E/odoo/service/model.py", line 97, in wrapper

    return f(dbname, *args, **kwargs)

  File "/home/shar/Projects/odoo-11E/odoo/http.py", line 335, in checked_call

    result = self.endpoint(*a, **kw)

  File "/home/shar/Projects/odoo-11E/odoo/http.py", line 936, in __call__

    return self.method(*args, **kw)

  File "/home/shar/Projects/odoo-11E/odoo/http.py", line 515, in response_wrap

    response = f(*args, **kw)

  File "/home/shar/Projects/odoo-11E/odoo/addons/web/controllers/main.py", line 935, in call_button

    action = self._call_kw(model, method, args, {})

  File "/home/shar/Projects/odoo-11E/odoo/addons/web/controllers/main.py", line 923, in _call_kw

    return call_kw(request.env[model], method, args, kwargs)

  File "/home/shar/Projects/odoo-11E/odoo/api.py", line 689, in call_kw

    return call_kw_multi(method, model, args, kwargs)

  File "/home/shar/Projects/odoo-11E/odoo/api.py", line 680, in call_kw_multi

    result = method(recs, *args, **kwargs)

  File "/home/shar/Projects/odoo-11E/odoo/addons/base/module/wizard/base_export_language.py", line 38, in act_getfile

    tools.trans_export(lang, mods, buf, this.format, self._cr)

  File "/home/shar/Projects/odoo-11E/odoo/tools/translate.py", line 711, in trans_export

    translations = trans_generate(lang, modules, cr)

  File "/home/shar/Projects/odoo-11E/odoo/tools/translate.py", line 998, in trans_generate

    out.append((module, type, name, id, source, encode(trans) or '', comments))

  File "/home/shar/Projects/odoo-11E/odoo/tools/translate.py", line 133, in encode

    assert isinstance(s, pycompat.text_type)

AssertionError

Any solution?