News in 3.99.6
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* Reduce a lot the number of translatable strings (especially in *.lang files),
  to translate only what makes sense. 630 -> 93 translatable strings!
* Build: remove ENABLE_NLS option, always support gettext translation, to
  simplify the code.
* Fix bug in gtk_source_view_indent_lines().
* Fix bug to read GtkSourceView 4 *.lang and style scheme files, not those from
  GtkSourceView 3.
* Code refactorings to prepare for the namespace change.
* Improvements to the syntax highlighting of: Vala.
* Improvements to the Visual Studio builds.
* Various other small improvements.
* Translation updates.