Linux/FreeBSD/macOS: Implement language selection settings (#1253)

* Implement Language selection into settings
Initial commit to create a new tab in PreferencesNotebook for
Language selection. By default, if nothing is chosen, it uses the
current behaviour of using the language from system environment
variables. If another language is chosen from the settings, it is
saved into the Configuration.xml and this is used instead.

* Fix SetStringSelection() assert issue on macOS

* Add header include to fix build

* Add current language pack, authors and way to use literal strings

* Translations also for FreeBSD

* Minimal GTK3 WX build on FreeBSD requires wxGraphicsContext

* Get Preferences properly instead of workaround function

* Use WrapSizer instead of BoxSizer for author line
This forces long author lists to be put on a new line, reducing
the need to increase window width.

* Update Finnish translation

* Borrow translation from IDM_LANGUAGE where it makes sense

* Remove colon and thus unneeded function

* Simplify Language tab layout

* Reintroduce macOS specific fixes to Forms.cpp

* cleanup

Translations/Language.zh-cn.xml

@@ -1636,6 +1636,9 @@
     <entry lang="zh-cn" key="IDC_LINK_KEYFILES_EXTENSIONS_WARNING">有关使用第三方文件扩展名的重要信息</entry>
     <entry lang="zh-cn" key="IDC_DISABLE_MEMORY_PROTECTION">为辅助功能的兼容性禁用内存保护</entry>
     <entry lang="zh-cn" key="DISABLE_MEMORY_PROTECTION_WARNING">警告：禁用内存保护会显著降低安全性。仅当您依赖辅助功能工具（如屏幕阅读器）与VeraCrypt的UI交互时，才需启用此选项。</entry>
+    <entry lang="en" key="LINUX_LANGUAGE">Language</entry>
+    <entry lang="en" key="LINUX_SELECT_SYS_DEFAULT_LANG">Select system's default language</entry>
+    <entry lang="en" key="LINUX_RESTART_FOR_LANGUAGE_CHANGE">For the language change to come into effect, VeraCrypt needs to be restarted.</entry>
   </localization>
   <xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
     <xs:element name="VeraCrypt">