Add Vietnamese translation (#10929)

* Add Vietnamese localization file for OrcaSlicer

* add Vietnamese po file

* Add Vietnamese language support in GUI (#11000)

- Added Vietnamese (vi_VN) to the language mapping in GUI_App.cpp.
- Updated Preferences.cpp to include Vietnamese in the language combobox and display its name in Vietnamese (Tiếng Việt).

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Co-authored-by: SoftFever <softfeverever@gmail.com>

src/slic3r/GUI/GUI_App.cpp

@@ -6787,6 +6787,7 @@ wxString GUI_App::current_language_code_safe() const
         { "tr", 	"tr_TR", },
         { "pt", 	"pt_BR", },
         { "lt", 	"lt_LT", },
+        { "vi", 	"vi_VN", },
 	};
 	wxString language_code = this->current_language_code().BeforeFirst('_');
 	auto it = mapping.find(language_code);