A Unix path can contain any bytes (commonly thought of as characters) except 0. A file name can contain any bytes except 0 and 47. In a lot of cases, the bytes can be decoded as valid UTF-8; but that's not universally true. It's just not right to throw arbitrary bytes from the FS at Gfx::Painter/Gfx::Font an expect it to deal.

USERSPACE(26) ASSERTION FAILED: m_ptr[offset] >> 6 == 2
../AK/Utf8View.cpp:210
[FileManager(26:27)]: Terminating due to signal 6
[FinalizerTask(3:3)]: 0xdeadc0de  Kernel::Scheduler::switch_now() +64
0xdeadc0de  Kernel::Scheduler::yield() +85
0xdeadc0de  Kernel::Thread::yield_without_holding_big_lock() +36
0xdeadc0de  Kernel::Process::do_killself(int) +191
0xdeadc0de  Kernel::Process::sys$kill(int, int) +258
0xdeadc0de  syscall_handler +1158
0xdeadc0de  syscall_asm_entry +29
0x080c9fac  raise +22
0x080480bd   +13
0x080c6b2c  tolower +0
0x080dbf53  AK::Utf8CodepointIterator::operator*() const +147
0x080a2bdd  Gfx::Font::width(AK::Utf8View const&) const +73
0x080a2c34  Gfx::Font::width(AK::StringView const&) const +30
0x08056f83  GUI::AbstractTableView::update_column_sizes() +491
0x08057dc0  GUI::AbstractTableView::did_update_model(unsigned int) +30
0x08078a33  GUI::Model::for_each_view(AK::Function<void (GUI::AbstractView&)>) +109
0x08078a8a  GUI::Model::did_update(unsigned int) +66
0x0807d0cf  GUI::SortingProxyModel::resort() +271
0x08078a62  GUI::Model::did_update(unsigned int) +26
0x0806f1d2  GUI::FileSystemModel::update() +118
0x0806d035  GUI::FileSystemModel::set_root_path(AK::StringView const&) +53
0x0804c5c6  DirectoryView::handle_activation(GUI::ModelIndex const&) +208
0x080583d7  GUI::AbstractView::activate_selected() +93
0x08058486  GUI::AbstractView::doubleclick_event(GUI::MouseEvent&) +142
0x080c48d8  Core::Object::dispatch_event(Core::Event&, Core::Object*) +74
0x0809226c  GUI::Window::event(Core::Event&) +1070
0x080c48d8  Core::Object::dispatch_event(Core::Event&, Core::Object*) +74
0x080bef13  Core::EventLoop::pump(Core::EventLoop::WaitMode) +307
0x080bf091  Core::EventLoop::exec() +43
0x0805b45f  GUI::Application::exec() +37
0x0804b49b  main +12432
0x0804bfae  _start +94