Other projects like Rhythmbox rely on GStreamer and enjoy native charset fallback by GST_TAG_ENCODING.

It seems to be affordable patching with g_getenv() and some of UTF-8 conversion facilities. But,

• I can't make decision where those lines of patch inserted. From inside of C function metadata_get_title() to the boundary between C# Metadata class and interface layer.
• I don't know how to code C#. Classes and methods of Mono is big challenge to me.

In the long run, such builtin utility shall be replaced by GStreamer thing.

Applying CSS box model to GTK+

Among all the properties in CSS box model,

• only GtkBorder is present in GTK.
• property padding is on list of TODO, AFAIK.
• property margin is missing 'til this time.

GtkAlignment was said to implement padding. Why not GtkContainer?

GtkContainer has ::set_border_width API. But the argument is not a GtkBorder but a integer. ::set_border with GtkBorder must implemented.

One of idea is to build GtkStyle from CSS text and set the style to a widget. GtkStyle possible created by a GtkRcStyle, and I don't know how to make a good GtkRcStyle, yet. GtkRcStyle itself should contain all the properties of CSS text.

libcroco the SAC implementation may be the parser of CSS to RC.